10.7.3 mail alias not populating header correctly?

I use a number of aliases in my e-mail, mostly for different discussion groups.

I don't remember when this started but...

When I send a message from Mail to a group using an alias, it gets bounces. "From" is populated with the account address (not an alias) and the alias address shows up nowhere in the header.

When I send a message from Google web mail, "From" is populated with the alias.

I have my own domain name, and am set up as imap.

Thanks