Can't send emails. The server response was: 1060208403.

Question

Nobody in my office can send emails today. All eight of us can access the Internet and send emails normally on our computers.
When attempting to send a message I get the following error message:
Cannot send message using the server mail.ourserver.org
The server response was: 1060208403
We are using Port 26 to send email.
Our web/email host did not find any issue with the mail server or with our account. They suggested it's a problem with our mail client.
Any ideas?

Answer 1

It would appear somebody needs to connect into your network and/or your client system(s), and to dig around.
So there are presently eight separate systems have eight separate cases of the same problem, and your email vendor says it is a client issue?
Ok; that would not be my first guess here.
An initial suspicion would involve hardware common to all of the client systems. At your network, wireless, router(s) or switch(es) and/or at your firewall. At the connection with your network and the rest of the Internet.
And a look at the email vendor and the vendor's server(s), since the vendor is also common to all eight clients here.
Has anyone been working with your DNS, firewall or other such? (I'm going to assume not, but it is worth a mention.)
Use of port 26 is odd. I'd expect port 25 or port 587. Can you confirm that port? Port 25 is comparatively unusual for sending email of late; many entities now use 587.
Are you running a local email server? If so, that could be having an issue. I'd expect to see a local SMTP email server connect to the next SMTP server via port 25 or potentially via 587.
Can the clients make connections to other networks and servers; are other web servers and sites accessible? If so, that tends to rule out the common pieces of hardware; hunks such as the firewall and the Internet connection.
There's no obvious translation of that specified error code; that's not an SMTP error, nor is it visible anywhere on the 'net. It may well be something from the client, or something from the network somewhere.
Here is Thunderbird troubleshooting information, which might give you some ideas of where to look here (even though you're probably using Mail.app):
http://kb.mozillazine.org/Cannotsendmail
If you have an email server running locally, the spectrum of potential problems becomes rather larger.