Error: SMTP Error 504

What's Causing This Error

This error is similar to a 502 error. If an SMTP command parameter is not implemented in the MTA (Message Transfer Agent) configuration, you may run into this error.

Solution - Here's How To Resolve It

Review the failed request and analyze the SMTP command parameters to resolve the error. Afterward, open the SMTP MTA configuration and configure the MTA to accept the parameter, or try to send the email without using the command causing the error.