I've setup a sendmail, dovecot and fetchmail combo on a server that can only be accessed from the LAN. Basically this is how it works:

1) Fetchmail retrieves mail from the "real" external email server (let's call it mail.test.xyz) and delivers it to the local users' mail spool.

2) Sendmail is used to send emails.

3) Dovecot provides the pop3 and imap access to local users' mail spool.

Everything works fine, except for the fact that the external IP for this server is part of a blacklisted domain in the Spamhaus SBL.

I've masqueraded mail from the local server to show it's from test.xyz.

The SMTP login for users on the external email server is in this format: username@test.xyz; Whereas SMTP login on the local server is just username.

I need to know if there's a way to use the external email server to process mails to domains other than test.xyz while letting it handle local mails as normal. Additionally, I need to somehow rewrite the user portion of remote server authentication from username to username@test.xyz.

What do I have to configure? Sendmail, procmail, both? And how? Any assistance is highly appreciated.