Understanding smtp server response

Hi,
I like to check with anyone who might be able to advise me on the problem below.
I have a servlet which uses JavaMail to send out emails to a smtp server. During our peak access hours, we have many requests to send out emails, after a while my application went into CLOSE WAIT accumulation and finally my application server stops processing.
When i did a thread dump, i found quite a number of threads still occupied with the process below. Does it mean that this is a symptom of network bottleneck where the smtp server is not responding as fast to the client and hence holding up the rest of the threads ? Is JavaMail send() method a synchronous call that has to wait for a server response before the thread is released ? Or is this a case of my network problem ?
"ExecuteThread: '11' for queue: 'default'" daemon prio=5 tid=0x39fb28 nid=0x18 runnable [0xbf980000..0xbf981a38]
at java.net.SocketInputStream.socketRead(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:85)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:181)
at java.io.BufferedInputStream.read(BufferedInputStream.java:199)
at com.sun.mail.util.LineInputStream.readLine(LineInputStream.java:56)
at com.sun.mail.smtp.SMTPTransport.readServerResponse(SMTPTransport.java:929)
at com.sun.mail.smtp.SMTPTransport.issueCommand(SMTPTransport.java:878)
at com.sun.mail.smtp.SMTPTransport.finishData(SMTPTransport.java:820)
at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:322)
at javax.mail.Transport.send0(Transport.java:164)
at javax.mail.Transport.send(Transport.java:81)

Thank you very much for the advise. It has helped me a lot.
Do you mind if i ask a few more questions on smtp ?
I do not know why i keep getting the error below when trying to send email to external email addresses like yahoo.com ?
nested exception is:
javax.mail.SendFailedException: Invalid Addresses;
nested exception is:
javax.mail.SendFailedException: 550 Relaying is prohibited
I checked the firewall setting and it has already been granted for my server to reach the smtp server via port 25 when i check using telnet command. Do you have any idea what else i need to do ?
Thanks

Similar Messages

Email error "Server Response: '451 Invalid Smtp l...

I am repeatedly getting this message when sending mail from smpt mail.btintenet.com :
Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Subject 'Re: Case AVG#0000334806: [ ref:00D4000000086fU.5004000000ADEMJ:ref ] RE: AVG technical support - e-mail scanner gmail issues', Account: 'mail.btinternet.com', Server: 'mail.btinternet.com', Protocol: SMTP, Server Response: '451 Invalid Smtp line - Should end with CRLF', Port: 25, Secure(SSL): No, Server Error: 451, Error Number: 0x800CCC0F
I am also getting "password rejected" message. I have twice re-set my original password on the Servers page of my OE bt account, also in the smtp settigns. i have visited my BT-Yahoo inbox and find I am still logged in there, and can receive from there in OE.
Solved!
Go to Solution.

NOT SOLVED YET sorry, it is much more complicated:
All mails I send out of OE from either bt or gmail accounts, are sent with bt smtp server: mail.btinternet.com . Outgoing mail is not scanned by AVG n any case, and the problem occurs whether AVG email scanner is enabled or not.
All the HTML mails that I have created and sent to myself at least for the past month, whether from bt account to gmail or vice versa, or just bt to bt, cause error 451 etc when forwarded as attachments after I have received them.
BUT the problem does not occur when the original, forwarded email was written in Plain text, even if the mail in which it is forwarded is HTML.
Also, those same HTML mails that later cause the error when forwarded after they have been received, can be forwarded as attachments OK from the Sent box, but not from the Inbox after receipt.
But both HTML and plain text mails other people have sent me CAN be forwarded OK as attachments from either account.
Mails sent to myself from the BY Yahoo and gmail webmail can both be forwarded again in OE to bt without any error (but those from bt to bt end up in BT Yahoo spam folder, until manually checked as "Not Spam").
Is something in the bt smtp server causing the problem, since all mails I send from OE go through that server ...?

How to check whether a SMTP server is supporting Authentication or not

Hi All,
We are using Java Mail API 1.3.1/1.3.2 to send the messages. some of the SMTP servers that we use are supporting authentication and some of them are not.
As the SMTPTransport.supportsAuthentication() is not available only in Java mail API 1.4.1, we are identifying the SMTP server whether it is supporting authentication or not in the following way.
Socket clientSocket = null;
InetSocketAddress socketAddress = null;
OutputStream outStream = null;
InputStream inStream = null;
InputStreamReader inReader = null;
OutputStreamWriter outWritter = null;
try
clientSocket = new Socket();
socketAddress = new InetSocketAddress(host, port);
clientSocket.connect(socketAddress, timeout*1000); // convert timeout from second to miliseconds
// 1: now try to execute the given command by passing that on Out-Socket
outStream = clientSocket.getOutputStream();
outWritter = new OutputStreamWriter(outStream);
outWritter.write("ehlo localhost" +"\n");
outWritter.flush();
// 2:Read output of above command
inStream = clientSocket.getInputStream();
inReader = new InputStreamReader(inStream);
// This array limit would be fine to get "AUTH" extension of smtp server.
char[] arr = new char[16384];
StringBuilder strBuilder = new StringBuilder();
inReader.read(arr);
for(int i=0; i< arr.length; i++)
strBuilder.append(arr);
System.out.println(METHOD_NAME + "SMTP server response for ehlo localhost command ->"+strBuilder.toString());
// The output EHLO command comes like below :
// ehlo localhost
// 250-ap9058pc.us.oracle.com Hello ap614ses.us.oracle.com [130.35.33.43], pleased to meet you
// 250-ENHANCEDSTATUSCODES
// 250-PIPELINING
// 250-8BITMIME
// 250-SIZE
// 250-DSN
// 250-ETRN
// 250-AUTH GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN
// Since for XATUH ( like internal IP),
// we are not sure, so just checking for AUTH capability.
supported = strBuilder.indexOf("250-AUTH") >=0? true : false;
As shown in above code, we are issuing 'ehlo localhost' command to SMTP server, if the response i. 'strBuilder' contains '250-AUTH' then we are assuming that it is supporting authentication.
But for one SMTP server the 'strBuilder' value is showing as '220 mail.durofelguera.com ESMTP Service (Lotus Domino Release 8.5.2) ready at Thu, 16 Feb 2012 13:57:20 +0100' only which is socket connection output but not 'ehlo localhost' command output.
where as the telnet test output is showing correct only as below
# telnet mail.durofelguera.com 25
Trying 172.20.16.65...
Connected to mail.durofelguera.com.
Escape character is '^]'.
220 mail.durofelguera.com ESMTP Service (Lotus Domino Release 8.5.2) ready
at 0
ehlo localhost
250-mail.durofelguera.com Hello localhost ([172.20.15.209]), pleased to meet
yu
250-HELP
250-AUTH LOGIN
250-SIZE
250 PIPELINING
AUTH LOGIN
The question is why the 'strBuilder' is not showing 'ehlo localhost' conad output where as the telnet test results are showing correctly, what is going wrong here?
Is there any other way to check that whether SMTP server is supporting authentication or not?
Edited by: sarojak on Feb 19, 2012 10:11 PM

There are so many things wrong with your code, it's hard to know where to start...
Basically, the problem is not as simple as you think it is.
For example, some servers might not allow authentication until you've issued
the STARTTLS command.
These days, essentially all servers allow authentication. You're probably better
off just assuming the server supports.

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.

try
MailMessage mail = new MailMessage();
SmtpClient SmtpServer = new SmtpClient("smtp.gmail.com");
mail.From = new MailAddress("[email protected]");
mail.To.Add("[email protected]");
mail.Subject = "Test Mail..!!!!";
mail.Body = "mail with attachment";
System.Net.Mail.Attachment attachment;
attachment = new System.Net.Mail.Attachment(@"C:\Attachment.txt");
mail.Attachments.Add(attachment);
SmtpServer.Port = 587;
SmtpServer.UseDefaultCredentials = true;
SmtpServer.Credentials = new System.Net.NetworkCredential("userid", "Password");
SmtpServer.EnableSsl = true;
SmtpServer.Send(mail);
Catch(Exception exception)
When i m run this part of code it throw an Ecxeption
Given Below is the Error..
The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.
Bikky Kumar

try
MailMessage mail = new MailMessage();
SmtpClient SmtpServer = new SmtpClient("smtp.gmail.com");
mail.From = new MailAddress("[email protected]");
mail.To.Add("[email protected]");
mail.Subject = "Test Mail..!!!!";
mail.Body = "mail with attachment";
System.Net.Mail.Attachment attachment;
attachment = new System.Net.Mail.Attachment(@"C:\Attachment.txt");
mail.Attachments.Add(attachment);
SmtpServer.Port = 587;
SmtpServer.UseDefaultCredentials = true; ///Set it to false, or remove this line
SmtpServer.Credentials = new System.Net.NetworkCredential("userid", "Password");
SmtpServer.EnableSsl = true;
SmtpServer.Send(mail);
Catch(Exception exception)
Given Below is the Error.. The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required.
Solution:
The error might occur due to following cases.
case 1: when the password is wrong
case 2: when you try to login from some App
case 3: when you try to login from the domain other than your time zone/domain/computer (This
is the case in most of scenarios when sending mail from code)
There is a solution for each
solution for case 1: Enter the correct password.
Recomended: solution for case 2: go to
security settings at the following link https://www.google.com/settings/security/lesssecureapps and
enable less secure apps . So that you will be able to login from all apps.
solution 1 for case 3: (This might be helpful) you need to review the activity. but reviewing the activity will not be helpful due to latest security
standards the link will not be useful. So try the below case.
solution 2 for case 3: If you have hosted your code somewhere on production server and if you have access to the production server, than take remote
desktop connection to the production server and try to login once from the browser of the production server. This will add exception for login to google and you will be allowed to login from code.
But what if you don't have access to the production server. try
the solution 3
solution 3 for case 3: You have to enable
login from other timezone / ip for your google account.
to do this follow the link https://g.co/allowaccess and
allow access by clicking the continue button.
And that's it. Here you go. Now you will be able to login from any of the computer and by any means of app to your google account.
Regards,
Nabeel Arif

Access SMTP Server Messages & Responses

I have the need to be able to send an email and a fax (via smtp) to two different servers. I've got the email portion set up, but I'm having trouble with the fax. The problem is that the RCPT TO: and the To: portion in the DATA: sections need to be different. I need to be able to see what I'm sending to the server and what the response I get back from the server on each individual line. Is this possible with JavaMail?
Example (first line = message sent to server, second line = server response):
This information was obtained by rolling my own smtp mail app. Please notice the differences between RCPT TO: and To:
=>HELO
=>250 sbfax001.stars-net.com Hello [12.28.86.153]
=>MAIL FROM: [email protected]
=>250 2.1.0 [email protected]...Sender OK
=>RCPT TO: "FAX=/NUM=1-806-345-2713/NAME=Wil Caetano/FROM=Kenan Dalley"@sbfax001.stars-net.com
=>250 2.1.5 "FAX=/NUM=1-806-345-2713/NAME=Wil Caetano/FROM=Kenan Dalley"@sbfax001.stars-net.com
=>DATA
=>354 Start mail input; end with <CRLF>.<CRLF>
=>From: Kenan Dalley <[email protected]>
To: Wil Caetano <[email protected]>
Subject: Test subject
Mime-Version: 1.0
...(etc)...
=>250 2.6.0 <[email protected]> Queued mail for delivery
=>QUIT
=>221 2.0.0 sbfax001.stars-net.com Service closing transmission channel

Ok. I see the getDebug(true) [and with 1.3.0 getDebugOut(InputStream)] to be able to see the messages to and from the server. I guess my remaining question is: Can I set the RCPT TO different from the To: in the DATA section with JavaMail?

How Client Browser Understand Server response

Hi Experts,
Iam new to java advance Technology. I hava a simple doubt, that "How Client Browser Understand Server response".
suppose if u open multiple Browsers and u typing same URL in all browser window(www.rediffmail.com). The server will generate response for requested resources. I dont no how the response will received by client browser without any conflit.
I need to know, whether the browser attach any ID to requested URL (or) any other machanism which helps the identification.
plz reply with example
Thank u

Hi praks_it,
"How Client Browser Understand Server response".
I dont no how the response will received by client browser without any conflit.
I need to know, whether the browser attach any ID to requested URL (or) any other machanism which helps the identification.
The answers to all the above of ur questions is the HTTP (Hyper Text Transfer Protocol).
It is a mechanism developed and documented by the W3C (World Wide Web Consortium) which specifies all needs for internet and browsers.
Check out the following links and u'll gain more on the subject :
1) http://www.google.co.in/search?hl=en&lr=&oi=defmore&q=define:HTTP
2) http://www.w3.org/Protocols/rfc2616/rfc2616.html (recommended).
Hope this helps.
Cheers !!
Sherbir

Server Response: 550 5.7.1 Unable to relay

SBS 2011 I have exchange 2010,
Internally Outlook send/ Receive working fine-- Local Ip address.
Owa Send/Receive working fine.
But remote user can receive the Emails, But cant send the emails.
Subject 'tes'
Server Error: 550
Server Response: 550 5.7.1 Unable to relay
Server: 'xxx.xxx.xxx.xxx'---- Public IP address
Windows Live Mail Error ID: 0x800CCC79
Protocol: SMTP
Port: 25
Secure(SSL): Yes
How to fix this issue ?

Hi,
Did you create a relay connector to allow to relay in Exchange? About how to create a relay connector, you can refer to the following article.
How to Configure a Relay Connector for Exchange Server 2010
http://exchangeserverpro.com/how-to-configure-a-relay-connector-for-exchange-server-2010/
Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make
sure that you completely understand the risk before retrieving any suggestions from the above link.
To allow a device to use Exchange to relay a message to an outside recipient, you also need the ms-Exch-SMTP-Accept-Any-Recipient attribute.
Get-ReceiveConnector -Identity relayconnector | Add-ADPermission -User "NT AUTHORITY\ANONYMOUS LOGON" -ExtendedRights "ms-Exch-SMTP-Accept-Any-Recipient"
Best regards,
Belinda
Belinda Ma
TechNet Community Support

LMS 3.2.1 changing smtp server

Running lms 3.2.1 CS 3.3.1 on Windows 2003
I need to point the LMS server to a new mail relay, but when I make the change in
CS->SERVER->Admin->System Preferences smtp server
It claims to have made the change successfully but the old IP address remains.
I made a successfull change days before. Any help/thoughts appreciated?

Afroj,
Thank You for the response. Unfortunately I am unable to provide the regdaemon.xml as this is a closed system.
The regdaemon.xml file shows the old ip address that is displayed in the gui, however when I try to update it through the gui, the smtp.log shows successfull validation of the smtp service using the updated ip address.
I understand that this may not be resolvable without me providing this file and I can open a TAC case if necessary.
Can I edit the regdaemon.xml file directly to replace the ip address?

Fixing the SMTP server of localhost

I have installed the role of the SMTP server in my VPS and it's okay as you see there is a red mark on.
screenshot : prntscr .com/46tup6
(remove the space in the link between the "r" and ".", my account is not verified to post links) i want to fix this problem and need tomake the SMTP working normal.
I think only can you can help me fix this hope you answer me soon!
Thanks,

Hi MalikMax,
Did you confirm your SMTP configuration completed? You can refer the following related third party article to complete your configuration first.
How to set up an Internal SMTP Service for Windows Server 2012 Essentials
http://blog.powerbiz.net.au/exchange/how-to-set-up-an-internal-smtp-service-for-windows-server-2012-essentials/
More about the IIS question please post to the IIS forum.
IIS support forum
http://forums.iis.net/
Thanks for your understanding and support
Hope this helps.
*** This response contains a reference to a third party World Wide Web site. Microsoft is providing this information as a convenience to you. Microsoft does not control these sites and has not tested any software or information found on these sites;
therefore, Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. There are inherent dangers in the use of any software found on the Internet, and Microsoft cautions you to make sure
that you completely understand the risk before retrieving any software from the Internet. ***
We
are trying to better understand customer views on social support experience, so your participation in this
interview project would be greatly appreciated if you have time.
Thanks for helping make community forums a great place.

Remote server response was not rfc conformant

Hii folks, I have an issue with Exchange 2010 outbound mails.
Mails of some domains stuck in the queue with error "remote server response was not rfc conformant"
Appreciate your responds.

Hi,
According to your description, This issue is related to one of your clients. And I’d like to confirm if emails from the problematic user are stuck in the queue and other emails are delivered successfully.
If yes, I’d like to also confirm the version of the problematic user. Is it Exchange account? External user or internal user? Does it belong to a distribution group?
Additionally, I recommend to check the SMTP protocol log:
Understanding Protocol Logging:
http://technet.microsoft.com/en-us/library/aa997624(v=exchg.141).aspx
Configure Protocol Logging:
http://technet.microsoft.com/en-us/library/bb124531(v=exchg.141).aspx
Thanks,
Angela Shi
TechNet Community Support

Hotmail Plus' SMTP Server, anyone got it to work?

HI All,
Well, my gf just got a new macbook after I finally converted her to a mac, but now I am trying to set up her Hotmail plus account in Mac Mail. (because entourage is too slow)
Since microsoft is now offering a pop3/smtp service for their plus members, I decided to upgrade her account and pay the 20 bux.
so far so good.
Obviously, when I try to set up her hotmail account in outlook on windows, or in entourage in mac, it works perfectly.
Only thing is, I want to use it in mac mail.
so I got the necessary info from microsoft (after 20 emails back and forth, and them pretending not to understand my question...)
POP: pop3.live.com (port 995)
SMTP: smtp.live.com (port 25)
Note: make sure you check the box that indicates that your outgoing server requires authentication (in most mail clients this is not checked by default).
Username: your full email address
Password: your Windows Live ID password
After setting up in mac mail with this info, I can now receive emails perfectly.
The only problem is that I cannot send any.
the smtp server seems dead, or non existent.
So my question is, is there anyone out there who got this to work? in mac mail or any other pop3 program?
I think its not a port problem, as I send my own mail on my own smtp server on the same router using port 25 as well.
Lastly, I would like to clarify that I do understand that hotmail *****, but moving to gmail or anything like that is not an option for her, its too big a hassle atm, so please do not respond if that was going to be your response
Ok, I really hope someone out there made this work.
Cheers, and thanks for any help/suggestions in advance.

I have exactly he same problem. Trust me, I know how you feel about switching. When I saw the green star I thought I finally stumbled across the answer. Don't know why you marked the question answered. I have tried all the different ports, none of which worked. I'm so looking forward to solving this one.

My e-mails are not sending. "connection to SMTP server timed out." How do I get this working?

As of yesterday, I am receiving e-mails fine; however, unable to send. Everytime I try to send an e-mail, I get "Sending of message failed. The message could not be sent because the connection to SMTP server (my mail address) timed out. Try again or contact your network administrator.
I received help from lunarpages (they host my domain); however, they were unable to resolve the issue. They suggested something is blocking IP, or need to update Thunderbird, or there's a firewall there...
Help!!!
My clients are waiting for responses to e-mails!
Thank you.

To diagnose problems with Thunderbird, try one of the following:
*Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
*Restart the operating system in '''[http://en.wikipedia.org/wiki/Safe_mode safe mode with Networking]'''. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: [http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-including-safe-mode Windows 8], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Windows 7], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-vista Windows Vista], [http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx?mfr=true" Windows XP], [http://support.apple.com/kb/ht1564 OSX]
; If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Can port 25 be used for SSL-enable SMTP server ?

Hi,
Our customer is using port 25 for a SSL-enabled SMTP server without certificate. When our email client tried to connect to it, the following exception thrown:
DEBUG SMTP: exception reading response: javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection?
Since we don't want to ask our customer to change their port configuration unless absolutely necessary, we did some tests with our own SSL-enabled SMTP server that uses certificate. Here is what I got:
1) with port 25, got the same exception as above;
2) with port 465, worked fine;
3) with any other randomly pick up valid port, worked fine.
This made me wonder if 25 is for non SSL SMTP server ONLY. By the way, I'm using Javamail 1.3.4 and JSDK 1.4.2_02. My question is whether we can configure javamail so that port 25 can be used by SSL-enabled SMTP server?
Your help will be appreciated.

Yes, port 25 is intended for non-SSL servers only, although that doesn't
prevent a client from making a plain text connection and then using the
STARTTLS command to switch the connection to SSL/TLS. JavaMail 1.4
supports that usage.
You can configure JavaMail to use port 25 for SSL connections if you
really want to. JavaMail 1.3.x requires you configure an appropriate
socket factory to get SSL connections; you can configure whatever port
you want for use with that socket factory.

Can someone help me send mail using SMTP server?

I am having the most frustrating problem with SMTP outgoing email account. I use GoDaddy's Webmail (smtp.secureserver.net) and I receive all my emails through Apple Mail but I cannot send any. I haven't been able to for about two weeks now, aside from 3 or 4 fleeting windows of time when I could. Almost all of the time I try to send my emails, an error message says my outgoing account is offline. I've been on the phone with GoDaddy's tech support three times this week and did everything we could think of, which include these steps:
-Force Quit Apple Mail --> Restart Computer
-Change Default Ports to a specific one and uncheck "Use Secure Sockets Layer (SSL)"
-Check "Use only this server"
-Delete account completely from Apple Mail and re-load (which I had to go into Time Machine to recover messages, and lots a bunch in the process ugh!)
Nothing works! I depend on this email for my business, and I rely heavily on Apple Mail for this account. All of my other email accounts that I pull through Mail work fine, but of course they are not SMTP outgoing. Please help...I feel like I've tried everything and nothing works permanently.

At this point there are 2 possible causes to your problem:
Apple Mail
Connectivity between you and the SMTP server
I can't help with (1) as I use Thunderbird as my mail client (the biggest advantage being I can take my mail files and move between different versions of Mac OS X). If you suspect that your problem is due to Apple Mail, then using another email client to send a test message will prove the point. If it works, then the problem lies with Apple Mail and somebody else will have to chip in. If it still fails, then there may be connectivity issue between you and the mail server.
If you google "telnet smtp test" (without the quotes), you will find many articles showing you how to test an SMTP connection using telnet. Don't be put off by the fact that many of the articles assume you are running Windows. The only Mac bit you need to know is that telnet is a command line utility accessed via Terminal. The rest is generic.
Telnet will allow you to interact with the mail server a line at a time and show you exactly what and where the problem is. If you get an unexpected response from the server, go back to GoDaddy and show them the output. If you don't get any response at all (i.e. "telnet smtpout.secureserver.net 25" just hangs), then take it up with your ISP as you are simply not getting through to the server.
Good luck.

Sending Mail to a Comcast SMTP server

Have a MAC PRO and MacBook Pro on the same network both running OS 10.8.2 with two identical email accounts having identical settings. MAC PRO email accounts work as expected; able to send and receive emails. However on the MacBook PRO, unable to send emails from either account, only receive emails. I have the same email problem when using the MacBook PRO on different networks, like a Hotel.
Consistently get an error message stating “the sender address [email protected] was rejected by the server smtp.comcast.net.”
Tried deleting the accounts, restarting and entering new accounts; reinstalled OS 10.8.2; but no difference in the problem.
Worked with several layers of Comcast support, trying all sorts of Port and SSL settings, and confirmed my password works on Comcast webmail, but cannot determine why I cannot send email from one Apple computer when the other Apple computer works as expected. All they could do is blame Apple.
What is different about the MAC PRO (early 1998) and the MAC PRO (15-inch Late 2011}?

What was the SMTP error?
Comcast has messed up their outgoing server somehow. I got a message about "The sender address [email protected]" was rejected by the server smtp.comcast.net." This of course is absurd, since YOUR E-mail address has nothing to do with sending mail.
If that's the problem, you're going to have to call Comcast and repeatedly escalate the case until you can find someone with even a basic understanding of how E-mail works. I had to get a "supervisor" involved, and this person was still so ignorant that she had to call me back the next day after "researching" the problem and still proposing asinine attempts to resolve it. And it never did get fixed, by the time I left the location at which I needed to use Comcast.
You need to insist that your reply-to address is irrelevant for sending E-mail. If you're connected directly to Comcast's network (which you are when you're connected through your cable modem), you should be able to send through their SMTP server. Period. That's how Time-Warner and Verizon work, for example. The first thing you're going to hear is "Well, you're not using your Comcast E-mail account." IRRELEVANT. And why would anyone use the obscure Comcast-assigned E-mail address in 2013?
Good luck.

Understanding smtp server response

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