I have an cross forest Exchange environment where Domain A is running Exchange 2010 and Domain B is running Exchange 2013. We are in the beginning of migrating Domain A Exchange users to Domain B Exchange. One issue I have seen is when a user in domain B creates a meeting request for someone in Domain A, when the user in Domain A accepts the meeting request there is a double entry on the Domain B's calendar event, one entry for the GALsync and one for a user with Domain A's email address. 

If the creator of the event, the user in Domain B makes a change to the meeting that does not require acceptance from Domain A the event merges the Domain A's entry on the event to show just one user. However, if the creator makes any other changes that require the Domain A user to accept the double entry comes back. 

Basically is seems that when ever a message - accepting a meeting invite is received from domain A then the Exchange server on domain B does not see it as the GALsync contact and adds it to the event as a new users.

GALsync is working without error, Free-Busy lookup is working as well.

Thanks in advance.   

Hi Danny,

According to your description, I am still not quite sure about your issue. If there is a double entry on the Domain B's calendar event, one entry for the GALsync and one for a user with Domain A's email address, is this Calendar event totally the same event with the same time and date in Calednar?

Please confirm whether the issue happens to all users when receiving the cross forest meeting request. What's the exact meaning about one entry for the GALSync? Please confirm there is no third-party program installed between Domain A and Domain B. We can send and receive the meeting request only with OWA to have a test.

Regards,

This issue occurs for all users. There is not any third- party software installed between Domain A and Domain B. we can send and receive meeting request with OWA, I have also tested with Office 2010 but not Office 2013.