Over the past few months, I have been getting complaints from people who have not been receiving their confirmation emails. Today I started to look into the issue and I noticed that EVERY SINGLE person who is not getting email confirmations is using a Hotmail address. Is there a known issue with hotmail and xenforo? How can fix this? Edit: I've tried setting the -f parameter, changing smtp settings, and making sure that the email domain name from the site that I'm sending it from. The only other issue could be that i'm using a shared VPS host and have a shared IP address. I'm guessing that has something to do with it. I used the AOL Postmaster test to determine that I have a reverse IP. Whatever that means.