Office 365 - #5.1.1 SMTP; 550 No Such User Here

Hi,

We recently migrated over to Office 365 and everything is working fine apart from one user.

The user is able to e-mail internally and externally fine but sometimes when another user outside replies back to an e-mail that he has sent, the end user gets the following bounce back:

user@company.com
The e-mail address you entered couldn't be found. Please check the recipient's e-mail address and try to resend the message. If the problem continues, please contact your helpdesk.
The following organization rejected your message: company.com

user@company.com
company.com #<company.com #5.1.1 SMTP; 550 No Such User Here"> #SMTP#

The strange thing is, sometimes it will work fine but sometimes it bounces back. The user exists.

Thanks
MattTonerAsked:
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AmitIT ArchitectCommented:
Not Strange, it is due to Outlook cached old contact. Ask them to clear outlook cache and send again. To confirm, you can ask sender to provide header information from bounce back message and from header information you can find from which server it is bouncing back. 99% Outlook cache causes this issue.
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MattTonerAuthor Commented:
Hi, thanks for the reply.

I did think of that but I tested it by sending an e-mail to the users account and it worked fine. Then I sent another e-mail to the users account and it bounced back. Waited a few minutes and tried again and it worked.

I never previously sent an e-mail to the user.
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AmitIT ArchitectCommented:
Check the header information for the bounced back message and you will find, if it is bouncing back from mail server or not.
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