- I tried to send mail to someone, but got a "relaying denied" message (with the numbers 553 and/or 5.7.1).
- I can send mail to other people, but not to this person.
This answer applies if the mail error message resembles the examples shown here:
- This error usually indicates a problem with the mail configuration of the company or organization you are sending mail to.
- Typically, they have a primary mail server that exchanges mail with MIT, and they also have a secondary mail exchanger. The error happens when the secondary mail exchanger is misconfigured, and doesn't know that it is supposed to accept mail for the company.
- The solution is to telephone or fax the company or organization, and tell their computer administrators that their secondary mail exchanger is broken, and is not accepting mail.
Advanced users can verify the situation, by looking up the mail exchange (MX) records of the company in question.
- On a Unix or Macintosh computer, you can look up the MX records of company example.com by running the command
- On a Windows computer, you can look up the MX records of company example.com by running the command
The output of the MX lookup will show a number, and an internet domain name. The problem typically happens when the backup MX machine (the one with the higher number) forgets that it is supposed to accept mail for the primary domain.