Since upgrading from v14.x to v15.x, Some Outlook 2013 users have seen their recipients replaced by others in the messaging domain.
For example : jerry@mydomain.com becomes john@mydomain.com
The replacement occurs when sending.
It seems that the wrong recipient is always the next item in the Gloable Address List
The wrong recipient appears in the sent items and the server logs show that Outlook has requested sending to the wrong recipient.
The problem was reproducible with the same recipients.

I understood that Outlook's autocompletion played a role. Emptying the cache eliminated the problem. But not its reappearance in a random way, for random recipients.
As a result I have disabled the auto completion of Outlook.

The frequency of the problem was reduced but I had new cases since.
This time the problem was not reproducible. A second sends, to the replaced recipients the first time, was done correctly.

Without autocompletion, users rely on the global address book that is synchronized through sharepoint link.
We encounter the problem only between addresses of the only domain managed by the server. Addresses that are in the GAL.

We have never had such a problem for years, until the update of v14.x to v15.x

Has anyone else got the problem?
If yes, what info did I not show?

Thank you.