The problem, in case any one is interested, is that I think the list must be set with a very strict filter on the sender's email address.
I was trying to send from pass.my_real_email which is not a real email address (only the base part is, i.e., my_real_email; neither of which I want to post in the body of a post on a mailing list). I do this all the time though on other lists, and it has worked so far. I noticed that the email that shows up on the list is just the base email. But it does go through. But not this time, apparently. I have never handed out the base email address to anybody (until today) and I really don't like doing so. Need to come up with some other solution, I guess. Cheers, TRS-80
