Remote host said: 550 #5.1.0 Address rejected. [RCPT_TO]

Question

I got the message in the heading after sending an email from a Yahoo account to the address of an institution that had always admitted my correspondence (until yesterday).

• What does the above error imply?
• What is 550?
• What is #5.1.0?
• What does [RCPT_TO] means?
• Would you recommend a web source where this coding is explained in a simple and understandable fashion?
• Which action should I undertake to get my mail message through?

Answer 1

The 550 error is simply "Address rejected".

RCPT TO is the SMTP (Simple Mail Transfer Protocol) command to populate the recipient address, so this bounce is telling you that the recipient email address has been rejected. You can expect that this means the email box does not exist, but it may also be the user's box is full or {reasons}.

Normally you would check the spelling and/or contact the individual to confirm the email address.

Email is often (nearly always?) sent via SMTP. So the quickest way to get a handle on what is going on is to check an overview for SMTP such as Wikipedia, and then google for "SMTP Commands Reference" and "SMTP error messages"

Two random ones:

• commands: http://www.samlogic.net/articles/smtp-commands-reference.htm
• errors: http://www.serversmtp.com/en/smtp-error