Why are my messages being blocked by MessageLabs?

Question

I use MessageLabs to route all my outbound email for scanning. Now I am getting error messages to some or all of my emails, which do not explain the error. The errors are:

Your message to mail1.messagelabs.com was rejected.
I said:
RCPT To:
And mail1.messagelabs.com responded with
553 (#5.7.1)

What is the cause of this?

Answer

This behaviour is a not a fault in GMS. The problem here is that MessageLabs return a multi-line SMTP error. The first few lines of the error contain useful information about the problem, however the last line of the error, which is the one most mail servers will include in the failure message, only contains

553 (#5.7.1)

This does not contain any useful information for a user or an admin to be able to determine what is happening. At the least it should contain something to assist a user with what is the cause of the error.

Looking in your POST log for that day can give more information if you have sufficient logging enabled. The full errors look like this:

553-you are trying to use me
553-[server-xx.tower-1.messagelabs.com] as a relay, but I
553-have not been configured to let you [your IP address,
553-your hostname] do this. If you think you
553-should be allowed to relay, please contact
553-   support@messagelabs.com or +44(0) 1452 627 777.
553 (#5.7.1)

In this message "xx" is the number of the MessageLabs server in question. Also listed are your IP address and your hostname.

This error can be caused by a change being made to the IP you have assigned to your GMS server. Otherwise it may be an error on the part of MessageLabs. In either case, it is not a fault with GMS.

Keywords:MessageLabs 553 5.7.1