Hi all,
I'm no expert, but here's what I've experienced with spam.
I've had trouble with this, except that it's happened to me, not so much to my group. The problem is that some providers, particularly those associated with phone companies, but probably others also, have automated spam filters on their web sites. Unfortunately, some of these filters can't be turned off or disabled. I have to go into the spam folder on the web for my provider, and check all the messages as "not spam"; they come to my inbox within my email client, and I have to go through all of them. It's the only way I can temporarily clear out spam. Within the next week, the spam folder has another bunch of messages, some of which might be legitimate; also, some that were always legitimate get marked, again and again, as spam.
Mary