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).