CC Proxy can work as mail proxy server for Eudora.

CCProxy is an easy-to-use proxy server software. Full supports Windows 98/ME/NT/2000/XP. For more details of CCProxy, please click here. Also you can download it here for a trial.

Suppose email address is .
Mailbox account: support
Password:***********
SMTP address: smtp.youngzsoft.com
POP3 address: pop3.youngzsoft.com
Proxy server address: 192.168.0.1

Launch Eudora.
Menu"Tools"--> "Opitions"

Real name: input your own name.
Mail Server (Incoming): input proxy server ip address.
Login Name: support#pop3.youngzsoft.com##support#smtp.youngzsoft.com
SMTP Server (Outgoing): input proxy server ip address.

Note:
If your original SMTP server requries authentication,
Login Name = Your original name#Your original POP3 server address##Your original login name#Your original SMTP server address
else
Login Name = Your original name#Your original POP3 server address###Your original SMTP server address

Only the version after 01/06/2002 of CCProxy supports Eudora mail proxy. You can download this version here.