550-5.1.1 Bounce back messages

Lately, I have had a few of my users getting bounce back messages with the following message:
mx.google.com #550-5.1.1 The email account that you tried to reach does not exist. Please try 550-5.1.1 double-checking the recipient's email address for typos or 550-5.1.1 unnecessary spaces. Learn more at 550 5.1.1 https://support.google.com/mail/answer/6596 vc5si4454764vdc.14 - gsmtp ##
We are running Exchange Server 2007 with an Outlook 2007 client.
On one of my users Outlook client, I created a new Outlook Profile and the problem seems to have stopped. But, I have 3 other users having the same issue.
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Is the recipient address correct? Are the users using auto-complete to select the recipients address? Try typing in the email manually. If this works correctly then I would delete their .n2k file under their profile.

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Mr_AllenAuthor Commented:
Thanks netcmh

The majority of the time this happens is when they reply to incoming meesages. I will try this solution and let you know of the results.
Will SzymkowskiSenior Solution ArchitectCommented:
On one of my users Outlook client, I created a new Outlook Profile and the problem seems to have stopped. But, I have 3 other users having the same issue

As you have stated above if you re-created the Outlook profile then you are removing all objects that reference the profile i.e. AutoComplete (NickNames). I would say from experience that this is most likely the cause.

You can garuntee that if you deleted the Outlook profile and it corrected the issue for one user then this is not a server sided issue it is client sided.

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Mr_AllenAuthor Commented:
This is a good answer. I tried it on a few of my users and it worked.
Thank you for the grade. Glad I could help.
jagan pCommented:
This may be due to incorrect email id or any spell check error of email id
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