And one of the most "interesting" ones is Hotmail with people having set their spam settings to Max = "receive email only from the contacts in my address book". The emails from the board then ends up directly in the Junk mail folder. I have at least 5 queries per day as to why haven't people received their verification email when registering in a forum I have and the funny thing is that even if I reply since I am not in their contacts my reply ends up in the junk mail as well.
You could make an announcement first in your board and tell users to allow the particular address to send them emails. Then you can have a look whether the IP address that your server/domain has the reverse dns feature (look
www.dnsstuff.com). If not then contact your ISP and tell them you want that. Most anti spam filters look that thing first.
I hope this helps a bit.
