We have been noticing shared mailboxes going missing from within the users outlook.  E.G: I have FULL access to few mailboxes and I have added them in my Outlook.  I am online Outlook client and I noticed those mailboxes will disappear and I will have to re-add them and then they work for few days and then evaporate again. 

Anybody seen this????  Any logging I can enable on the mailbox to catch it???  thanks

In such crucial circumstance, You need to enable mailbox audit logging that let's you track logons to a mailbox as well as what actions are taken while the user is logged on.

Please refer to this PDF guide that explains in depth by covering all the required steps to enable mailbox audit logging and track every critical changes into real time : http://www.lepide.com/guide/enabling-exchange-2010-mailbox-auditing.pdf

Here is another informative article : https://technet.microsoft.com/en-us/library/ff461937%28v=exchg.150%29.aspx

Hi WildPacket,

Base on my knowledge, it seems like an outlook client issue.

I recommend you change another computer OR upgrade your outlook client to the latest version, and then check if there is the same issue.

Best regards,