New Exchange user can send email but nor receive it

Hi. I work as a sysadmin and have worked with AD/Exchange for years. Today I am seeing a problem I have never seen before and it's quite infuriating. We created a user in AD and his associated domain login is fine. We set up a mailbox for his account, which I had to change the primary SMTP email address for. But we have to do that for all their new startes so this is nothing untoward. The problem I have is that the user can send email (test emails from his account to mine work fine). However, I cannot send him an email. Nobody can. The following message (attached) is bounced back - seemingly related to MessageLabs. when I check MessageLabs, it would appear that this user is configured to receive email.

Pulling. My. Hair. Out.#

Many thanks.
PowerhousecomputingAsked:
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PowerhousecomputingAuthor Commented:
Hi. I work as a sysadmin and have worked with AD/Exchange for years. Today I am seeing a problem I have never seen before and it's quite infuriating. We created a user in AD and his associated domain login is fine. We set up a mailbox for his account, which I had to change the primary SMTP email address for. But we have to do that for all their new startes so this is nothing untoward. The problem I have is that the user can send email (test emails from his account to mine work fine). However, I cannot send him an email. Nobody can. The following message (attached) is bounced back - seemingly related to MessageLabs. when I check MessageLabs, it would appear that this user is configured to receive email.

Pulling. My. Hair. Out.

Many thanks.

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Sudeep SharmaTechnical DesignerCommented:
Attachment is missing it seems.

Sudeep
PowerhousecomputingAuthor Commented:
this was good advice
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