We have to block 25 port and not allow set rDNS in the future
Why I can't send email via 25 port?
Lots of spamer use 25 port to send mail. By default port 25 was forbidden by a firewall, please use 3rd party SMTP service with 465 or 587 port if you need send order email and register welcome email from your website. eg. Gmail, Hotmail
SMTP tutorial: How to send email via SMTP with PHP and Gmail / Hotmail
We tried manually approve open 25 port request and limit the mail send speed, but still got lots of SPAM abuse these days.
Updated on 03/10/2014: Lots of our IPs been null routed and server suspended by datacenter many times because of some VPS clients use it for SPAM, which cause hundreds innocent VPS clients effected, so we decided to block 25 port and not allow set rDNS in the future.
We recommend you send email via SMTP to avoid most SPAM issue and many other good reasons.
Here is a tutorial of send email via SMTP use 465 or 587 port, please take a look :
http://www.comfortvps.com/VPS/How-send-email-SMTP-PHP-and-Gmail-Hotmail.html
You can order our special openvz VPS for setup your mail server(25 port is open and rDNS set is allowed) if you really want use your own VPS for send email (NOTE: Please DO NOT use your server for bulk email(include newsletter) or SPAM, any SPAM abuse will cause VPS delete, There are no second chances.)