Recently Cox Communications began blocking SMTP port 25 
on all but their own mail servers. In some cases,sending 
mail with any other email account is impossible unless 
your mail host has opened an alternate SMTP port.  
If that is the case, you need to change ports in Eudora. 

First, look for a file in the Windows directory called 
"services" and open it with Notepad.(In XP, the path 
is C:\windows\system32\drivers\etc ) Change the following 
entries to the desired port, or add lines in the case 
of multiple installations, wi6th an ac6count requiring 
the default ports.

smtp               25/tcp    mail 

Next, look in the Eudora directory for the directory 
"extrastuff". In this directory is a file named 
"esoteric.epi". Drag or copy this file into the 
main Eudora directory. Start up Eudora, go to Tools: 
Options: Ports, and change the ports here.