[BlueOnyx:05518] Sendmail stops relaying email to valid local account 'user.name at domain.com' - no such user here!

[Jeff Jones]

Very strange problem today - typical Monday - what is it with mondays?

A user has a mailbox user.name at domain.com - all is well. Nothing is changed on the mail server.

Today I get an email from her google mail account, telling me that no email is getting through to her account where the email address is user.name at domain.com. Hover - weirdly - email sent to an alias user at domain.com IS getting through.

The next thing I do is try to send her an email - and immediately, I get a bounce back - the error back is - 'no such user here'!?

I can log in to her account via the webmail - no problems. 
I can send an email from her account to me - no problem.
But I can not send an email to her, using her username, because sendmail can't see this for some reason.

To resolve the issue I had to add 'user.name' in as an alias - even though this wasn't needed before.

I am concerned this might be an early sign of some horrible sendmail nasty - any one seen this issue before?

Any ideas?

Cheers,

Jeff

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