Sometimes people have problems with spam filters eating their forum emails. This can be a problem when activation emails get flagged as spam. Of course one solution is to simply tell your users to check their spam folders. But many forum admins want to be more proactive about spam filters and try to prevent the problem in the first place. It is important to realize that there are no definitive solutions to the problem of spam filters. The best you can do is avoid common red flags. There are a few red flags you can check with respect to your mail configuration: Reverse DNS One red flag is Reverse DNS (RDNS). The explanation for RDNS can be a little complicated. This is the most accessible guide I was able to find on the topic: http://www.enewsletterpro.com/support/Reverse_DNS.asp In following this guide, you need to examine the mail headers of an email that was sent from your forum. Look for the Received header which looks like this in their example: Received: from JUNTO.adcomplete.org ([126.96.36.199]) by … Then use this RDNS tool to perform RDNS on the IP address from the Received header: http://postmaster.aol.com/cgi-bin/plugh/rdns.pl The IP address should resolve to the host name in the Received header. If it doesn't match then your emails are failing RDNS and you need to contact your mail host. -F Parameter It has been suggested that enabling the -f parameter for emails can help if you are using the default mail server: Admin CP -> Home -> Options -> Email Options -> Email Transport Method SMTP Server It has also been suggested that using the default mail server is itself a red flag for spam filters, and that setting up a SMTP server for your forum can help the problem. If you have access to a SMTP server through your host or ISP then you can enter that information in your: Admin CP -> Home -> Options -> Email Options -> Email Transport Method Or here is a guide for using Google as your SMTP server: http://xenforo.com/community/threads/setting-up-google-as-smtp-server-for-your-xenforo.6180/ "From" Address Also make sure your Default Email Address uses the same domain as your web site: Admin CP -> Home -> Options -> Email Options -> Default Email Address This is the "from" address for outgoing emails. Some spam filters and even SMTP servers don't like it when these two don't match.