"E-mail address is no longer valid" using Office365

Hi Experts,

We are using exchange server online with Outlook 2010 as the client.  

Each time we try to send email to somone with an email address that match our domain we get an the error:

   "This eamil cannot be delivered to johndoe@companyco.com because the email address is no longer valid"

 Over the last few days, Outlook users are suddenly getting the 'green' email address and the above warning when attempting to REPLY to SOME of our internal staff (different people are problems for different users)

I've tried the common fixes

-Delete the auto-complete individual address

-Delete the whole auto-complete cache

-Remove person from contacts and re-add

-Use online instead of cached mode (a few seconds delay before email shows as no longer valid)

-Outlook Safe mode (a few seconds delay before email shows as no longer valid)

Email DOES always get delivered though

As best I can tell, the senders email is the correct one

The issue is not seen using Outlook Web App
Who is Participating?
XaelianConnect With a Mentor Commented:
Hi there,

If you remove the cache mode and afterwards enable it, it will query for the GAL, ... . But it takes some time.

There is also a problem that it can be that you get the green message with an out of office. Then you also need to do the same thing :).
How have you deleted the auto-complete individuel address?

By the following?
Click File, Click Options, Click Mail, scroll down to the Send messsages section.  Click the button that says Empty Auto-Complete List.  Click Yes on the message that asks if you are sure you want to empty the auto-complete list.  Click OK on the Outlook Options window, exit Outlook, then re-launch the application.

Afterwards try to redownload the GAL. I've had to do this a couple of times with users and this fixes the issue.
gs1ukAuthor Commented:
Hi There,

Currently im not getting the issue. Im removed the cached mode and made it online and restarted Outlook and I dint get the message. I put it back to cached mode and its not come up yet. Im going to monitor for couple of hours and see if not will use your fix.

Thanks for you time Xaelian.
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