Still struggling with Gmail & others blocking list messages

[Erica C.]

Gmail, Yahoo, etc. are increasingly blocking some list messages for a volunteer organization. Some members of the group then get scary bounce messages and think they're about to be dropped from the list.

I've been doing additional research and hope to find answers to any of my questions.

1) Does anyone know why this is happening?
2) Would it help if we were a HTTPS site instead of HTTP?
3) Would adding Domain Keys help? Or would they mess things up as mailing list messages come from different people?
4) Would SPF help?

Finally, if there's no hope is there an alternative to ezmlm-idx?

Thanks!
Erica