What do SMTP 500 errors mean?

The SMTP command used was not recognized, or is not supported by the protocol or the given SMTP server implementation.


  • Check the syntax of your last SMTP command and try again.
  • This error can arise if your command was too long. Try to make it shorter.

It’s quite possible that this error arises along with a  421 error or graylisting when an SMTP server is being used too heavily. It often comes up when using free SMTP servers, which limit the number of e-mails that can be sent through them each day. This should be resolved by using specialized SMTP servers (such as SendPulse SMTP Server).

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