500 error and solving it

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.

Solution

• 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).