The address for our SMTP service is smtp.socketlabs.com. The IP address for smtp.socketlabs.com can change frequently because we employ widely geographically-distributed SMTP servers for high availability. Please ensure that your connections to our services are not programmed with specific IP addresses and are properly resolving and connecting to smtp.socketlabs.com.
We accept connections on ports 25, 2525, 587, and 465. Please note that connections to port 465 require the use of implicit SSL.
If you must use a firewall to restrict your outbound SMTP traffic to specific IP addresses, the following is a list of IP addresses we may use from time to time. We do not send out notices if these IP addresses change so if you are having connectivity issues, please check back here.
220.127.116.11 **Added 10/17/2014
Those able to enter CIDR ranges to their firewalls should open up 18.104.22.168/20 as future upgrades may result in the inclusion of other IP addresses in this range.
If you are concerned about allowing outbound SMTP traffic (port 25) to any IP as an alternative to programming specific IPs into your firewall, you may want to consider allowing outbound traffic to the lesser-used port 2525 on any IP, and configure your applications to connect to us on port 2525 instead of port 25.
If you are having problems connecting to smtp.socketlabs.com, see our KB article on troubleshooting common connection issues: http://support.socketlabs.com/kb/105/