Exchange Mailboxes are disabling for an Organization upon which ADSync status is set as enabled

Problem: In the HC panel, Exchange Mailboxes are disabling automatically for a specific organization. The only specific setting on this Exchange Organization is that it has ADSync status set as enabled. What could be the reason for this behavior?

Reason: This is a typical issue that occurs only in a specific scenario where the Mail attribute on an AD User is synced from Source DC to the Target DC that is connected to Exchange Server.

What is Mail Attribute for Exchange Mailboxes?
Mail attribute is mandatory for Exchange Mailboxes and can never be empty as its value represents the email address of a user. 

Events that cause Mail attribute to become Not Set :

  • After every 24 hours, ExgSyncOperations_0 task scheduler is executed and makes the mailbox disabled in the HC panel.

Why Mail attribute value is changing from to <Not Set> on Active Directory connected to the Exchange Server?
AD Connect Sync has the ability to push AD User attributes/passwords from Source DC to the Target DC. If on local Source DC the value of AD-User's Mail attribute is <Not Set> then on the target DC as this empty value will be transferred, it will erase the actual value on AD-User of Exchange Mailbox which eventually will result in disabling of the mailbox.

How to resolve it?
To resolve the case, ensure that you are passing the proper value of Mail Attribute from Source DC to Target DC connected to Exchange Server. If the value of Mail attribute is Not Set on the Source DC then one must not pass this attribute in the AD Connect Sync tool. And get this removed from the AD Connect Sync tool SyncAttrubutes.xml file located at C:\Program Files\HCdirSync\SyncingAttributes.xml

Note: By default, Mail attribute is excluded from the SyncingAttributes.xml file.
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