How do I stop spam from being sent to our mailing list?
A common problem these days is people's email accounts being hacked, and spam and/or links to viruses being sent to everybody in their address book.
Including your mailing list.
One solution is to check all emails for spamminess, and when spam is found, send it back to the subscriber for approval.
If they reply to this self moderation message, the message will be released.
The self moderation allows your subscribers to override the spam filter when it is mistaken.