Yahoo Mail issue, able to recieve but not send.

Question

I sold my friend my Macbookpro running 10.5.3 and he is able to receive emails but not send them even though the MBP makes the sound like the email was sent. Yahoo says they are not reaching their server. I told him to repair disk permissions which may be a long shot and if that did not work to add a new user account and re setup the email account over again and see if they go out from there. Any other suggestions would be appreciated. I know I have had this issue before but it was just because my outgoing mail server was not typed in properly.
He says everything is correct. Could it be a port issue?

Answer 1

Please see if the Apple mail troubleshooting support article resolves this misbehavior. 
Sending is the SMTP path, which is the one that nobody new to mail can find — mail uses POP or IMAP for receiving, and SMTP for sending, and there are separate settings, servers and login credentials for each.  To get to the SMTP settings, Mail > Preferences > Accounts > select the failing account > Account Information > select Outgoing Mail Server (SMTP) to Edit Mail Server List > select the SMTP account > verify the settings for the server, that SSL/TLS is enabled (usually) or not (rare), and that your username and password are correct.  Like the POP or IMAP settings, these SMTP settings and credentials are also specific to your mail ISP, which means I don't know exactly what the required settings are here. 
With the way that mail pops up that infernal "do you want to cause yourself grief by changing your password?" dialog box on transient network errors, it's very easy to get an incorrect password set, too.
I'm not sure why you've listed web server, Linux, Apache and PHP in your posting.