What does "550 550 5.4.1 Relay Access Denied (state 14)." mean?

550 Relay Access Denied is often a catch-all response for when mail is rejected, commonly due to falling into a spam filter.

Reasons could include actual spam detection (bulk mailing, or perhaps an overzealous spam filter setting), or a misconfiguration on your Google Apps domain settings where your domain's MX records don't match what IP the server is connecting from (seems unlikely).

I would definitely mention it to the mail administrator of your corporation. You may have uncovered a configuration issue that is also preventing a bunch of other people's email from arriving properly, possibly losing your company business.

I can see the thread is quite old, but a simple Google search sent me here, so I hope it can help other people.

I saw this error message today (a mail sent from a gmail address to an office 365 enterprise address).

The error was just the person tried to send the mail to [email protected] instead of [email protected] :)

So, if you get this message, you can double-check the recipient's address you typed.

PS: sorry if my English is basic, I'm a French user!

This could also happen if your exchange server happens to fill up with logs that have not truncated. If you have an application that does your back ups of Microsoft Exchange and those back ups fail then they won't truncate. Your server well essentially fill up with logs and you'll run out of Disc space and then your server will stop receiving / sending emails. Careful though: The reaction on our exchange server is not always the same; sometimes it will allow intra-emails and other times not. Sometimes after four attempts we can send an outbound but we cannot receive an inbound or vice versa.