Are you following the requirements for running mailing lists responsibly? Please see:
Application Note: Guidelines for proper mailing list management (has replaced Basic Mailing List Management Guidelines for Preventing Abuse),
Mailing Lists -vs- Spam Lists,
Best Practices for Mailing List Management,
How Can I Manage My Mailing List Responsibly?,
and the many links on Best practices.

[Jeff G. added Application Note: Guidelines for proper mailing list management 2005/03/29. This Topic obsoletes the previous FAQ Entry: Am I Running Mailing Lists Responsibly?.]

I just copied this over into the original post done up by JeffG with Moderator hat on ... Then hit the Forum FAQ itself with an "Updated" comment.

Oops, you forgot to copy the links.