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Error 500: Syntax Error, Command Unrecognized

What Is Causing This Error?

‘Error 500: syntax error, command unrecognized’ in SMTP is triggered when there’s a communication mismatch between servers. The root causes include the receiving SMTP server not recognizing or supporting the specific SMTP command issued or the command itself being too lengthy.

Essentially, this error highlights a syntactical or command compatibility problem between the sender and the receiver.

Resolving the Error – Solution

To address SMTP Error 500:

  1. Begin by reviewing the SMTP command’s length. Ensure that the length is within the acceptable range defined by the SMTP protocol.
  2. Double-check the command’s compatibility with the receiving SMTP server. It’s crucial that the command is one that the receiving server acknowledges and can process.
  3. Consider disabling your anti-virus software. In some instances, anti-virus software might interfere with the SMTP communication, leading to this error.
  4. Examine server logs for any additional clues or detailed error messages. Sometimes, logs can offer more specific pointers about what part of the command the server took issue with.

That’s it! Now you know the common causes of the SMTP 500 error and how to resolve it.

If you’d like to learn how to troubleshoot other common errors, check out the following tutorials: