Since many isps and VirusScan both block port 25, the only way to send mail in these instances is to use the submission port 587. Eudora version 6.2.3.4 has a box to check called “Use submission port (587)”. However, when using tcpdump to watch packets on port 587, it can be seen that Eudora does NOT, in fact, use port 587, but continues to use port 25. The solution is to edit the eudora.ini file and add a line. After the UseSubmissionPort line, add smtpport=587. These lines should look like this:
UseSubmissionPort=1
smtpport=587
After saving and restarting Eudora, mail is sent on the correct port.