Server 2008R2 / Swop over 2010

Hi Everyone,

Im having an issue that I cannot seem to work out! We have a mailbox that only certain people can have access too. In our AD we have a Worldwide Security group titled paysheet email access.

This morning I added a new user to this security group so I could open the payroll mailbox on thier report. However once I proceeded to expand the mailbox I got the user does not somebody permission.
Then approx 4 hours later the user can access the mailbox (I saw thier outlook account add the folders by itself).

This is an issue all for us because the user needed access to the box right away. To receive around this I had to wood onto the payroll acount and donate the user right to the mailbox/inbox etc via permissions. Only after could they access the mailbox.

Im wondering if this would be an ADVERT or an Exchange issue? Has anyone come across this before?

Any help would be great!

Source: http://feeds.spiceworks.com/~r/SpiceworksCommunity/~3/P-0rBG51O1o/191130-server-2008r2-exchange-2010