Occasionally you may find your mail server on blacklists either because of some random event or because it was compromised briefly and ended up sending out some not-so-invited email to people which in turn was reported.

Firstly you'll probably want to see if your server's IP is on any blacklists. This can be done via the Blacklist checker on MXToolbox.

There isn't an all encompassing removal method anywhere but I will detail (alphabetically) the main blacklisting sites on here so getting to their removal pages will be much easier than trying to search for them all individually.

AOL Postmaster - Delisting Page

Back Scatterer - Delisting Page
Not a recommended blacklist. Charges for delisting. Appears to be the same company as UCE Protect.

Barracuda - Delisting Page

Cloudmark (CSI IP) - Delisting Page

Composite Blocking List (CBL) - Delisting Page

Google - Delisting Page

Hotmail - Delisting Page

Invaluement Sender's IP DNSBL (ivmSIP) - Delisting Page

Lash Back - Delisting Page

Not Just Another Bogus List (NJABL) - Delisting Page

Passive Spam Block List (PSBL) - Delisting Page

SORBS - Delisting Page
Not a recommended blacklist. Charges for delisting.

Spam Cannibal - Delisting Page (click Contact)
Automatically blacklists any dynamic looking hostnames.

SpamCop - Delisting Page

Spamhaus - Delisting Page

Tiopan - Delisting Page