I have a contact group with about 60 or so contacts in it. I send out regular mass emails to them. A couple of people have reported never receiving some of the emails. They will regularly receive them, but then never get one. I never get an error notification, it is not in their spam boxes, and as far as I know it doesn't come later.
Other than the two who reported it to me, I have no way of knowing who else hasn't been receiving email.
The last two times it has happened the problem has been with yahoo mail users. However, once I never got an email that my professor sent to the class even though my email address was on the last and I had been receiving class emails from her regularly. I was using my zimbra address at the time.
I have access to zimbra webmail through my school.
Sorry for the double post, but I believe that I posted in the wrong forum before.