Remote host said: 511 sorry, recipient address has invalid format (#5.1.1 - chkuser)

[QH]

When an outside user tries to email a mailbox on our organisation, she
gets the following error: Remote host said: 511 sorry, recipient
address has invalid format (#5.1.1 - chkuser)
Giving up on <IP address>

I have been unable to find much information on this. Can anyone here
advise?

Many thanks.

[Nuevo]

Are you certain that the user address is being input correctly. Does this
happen with all senders or just one?

Nue

Post by QH
When an outside user tries to email a mailbox on our organisation, she
gets the following error: Remote host said: 511 sorry, recipient
address has invalid format (#5.1.1 - chkuser)
Giving up on <IP address>
I have been unable to find much information on this. Can anyone here
advise?
Many thanks.

[Andy David - MVP]

Post by QH
When an outside user tries to email a mailbox on our organisation, she
gets the following error: Remote host said: 511 sorry, recipient
address has invalid format (#5.1.1 - chkuser)
Giving up on <IP address>
I have been unable to find much information on this. Can anyone here
advise?
Many thanks.

Thats not an Exchange error.
What SMTP gateway is between the Exch Server and the Internet?

[QH]

The address is entirely correct. I have tested it and it resolves
perfectly using the GAL. Between the email server and the internet
there is (in this order): an Exchange front-end server; a content
monitoring server running Mailmarshall (similar to Mailsweeper); and an
Icritical server that is an externally run service to check for spam.

Post by Andy David - MVP

Post by QH
When an outside user tries to email a mailbox on our organisation, she
gets the following error: Remote host said: 511 sorry, recipient
address has invalid format (#5.1.1 - chkuser)
Giving up on <IP address>
I have been unable to find much information on this. Can anyone here
advise?
Many thanks.

Thats not an Exchange error.
What SMTP gateway is between the Exch Server and the Internet?