I recently installed zpanel on my vps, everything seems to work just fine except my mail client. I kept sending out test emails to verify that everything was working properly. The first 2-3 emails were received in the inbox just as expected. As I started to send out more emails to other email providers I noticed that my emails aren't being sent to the inbox anymore. They are going straight into the spam folders. I tested with Yahoo and Gmail. Both of these providers are receiving my email in spam folders. I'm using RoundCube to send out the emails, I tried Outlook without any luck. Also, tried to reply to one of my own Craigslist ads using their encrypted emails and RoundCube nor Outlook seem to send the email I get the following error: This is the mail system at host control.yourdomain.com. #################################################################### # THIS IS A WARNING ONLY. YOU DO NOT NEED TO RESEND YOUR MESSAGE. # #################################################################### Your message could not be delivered for more than 4 hour(s). It will be retried until it is 5 day(s) old. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. The mail system : host mxi4f.craigslist.org[208.82.238.83] refused to talk to me: 554 [EAF21D23-0C43-4ADB-9D11-C1A0B394E968] Sorry we could not find address for server.basicoffer.co.uk. Please setup a forward DNS record: http://www.craigslist.org/about/help/rdns_failure It's important to me that I'm able reply to Craigslist ads as I do a lot of business over there. My vps is running Centos 6.5 X64