This can happen when the Subscriber is receiving email at one address but trying to send from another. The From: address must match the address on the Mailing List exactly.

For instance, if Joe signs up as [email protected], and later his email address changes to [email protected], then his posts will be rejected.

Maybe Joe's employer made the change without Joe realizing the difference. His old email address is forwarded to his new address, while all new emails from him are sent from the new address.

We have instructions to help resolve this issue.