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Diagnosing SMTP Connection Issues to SocketLabs

If you are having problems connecting to there are some basic tests that can be performed to diagnose the issue that is occurring.  It is important to understand that is designed as a highly available system.  Since the implementation of our highly available design we have achieved completely uninterrupted access to  

Even with perfect up time we often get support requests reporting that a connection could not be established. First, always check for any status alerts about any possible service interruptions at  If there are no alerts on our status page then check some of the most common causes of connection issues such as:

1) Anti-virus software

2) Firewalls

3) ISP Restrictions or Blocks

Anti-virus software often effects SMTP connectivity because virus and malware components are known for generating SPAM messages.  If you are having trouble connecting to, the first troubleshooting step is to disable anti-virus software and try again to connect.  Firewalls are another leading cause of SMTP connection issues. Firewalls can be software- or hardware-based and commonly block SMTP traffic by default.  Be sure to check any firewall, both software and hardware-based, that may exist between you and your connection to your ISP.  See our KB article on SMTP connections for more information about setting up your firewall to allow acccess to our SMTP delivery infrastructure.

Once you can confirm that your machine is able to reach outside of your local network on any of the SocketLabs supported ports (25, 2525, or 587), the last hurdle is ensuring that your Internet Service Provider allows for SMTP transmissions on the port you are utilizing in the settings for your application.  Virtually all ISPs in the United States have been known to block port 25. This includes even large scale providers like Comcast, Verizon, Cox, and Time Warner as well as most smaller regional ISPs, so if you can't connect on port 25 be sure to try alternate ports 2525 or 587.

If you think you should have a clear path to open connections to but you are still having issues, the root cause may be compatibility with your application.  Double check your settings to make sure that is set as the SMTP server.  In order to test the true capability of your machine being able to establish a connection to, we have to eliminate the application from the equation and utilize an operating system level tool such as Telnet.

For more advanced troubleshooting information please see our in-depth blog post about SMTP connectivity diagnostics: Diagnosing SMTP Service Connection Issue

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