My question is: I believe the event 1016 is the manager mailbox trying to communication with the store.What/who is the "invalid sender"? Can I fix this?Here's some details in case that one sentence above didn't tell you everything. ;-)Delegates in our email organization report that delegates in another forest are not receiving meeting notification. Also, meeting notifications are not always getting into the manager's calendar.It only happens when the delegates are sending on behalf of the manager. With no delegates invovled and across the same forests, all works well.Peoplehavingbeen showing up or (not) at meetings.It's all trickled down and I just can't seem to figure it out. I'll try to put the information I have been able to gather.There are two untrusted forest:mailuser@forest1.commailuser@forest2.orgForest1.com has1 manager and he has assigned a delegate. Delegate has Senda as permission, with Editor on Calendar and Tasks. Both manager and delegate are to receive a meeting request/update.Use Exchange 2007Outlook 2003Forest2.org hasthe same scenario.Uses Exchange 2007Outlook 2007Forest1 delegate sends meeting notification to manager in forest2. The email is delivered to the manager's mailbox in forest2, and the calendar may or may not get updated with (let's say) with tentative status on a new meeting.However the delegate in forest2 never gets a copy of the email.The following event is recorded in the Application log of the receiving Exchange 2007 server------ Event Type:WarningEvent Source:MSExchange Store DriverEvent Category:MSExchangeStoreDriver Event ID:1016Date:Time:User:N/AComputer:Forest2 MailServerDescription:The sender for event 1460628 mailbox GUID for (Exchange quid of Forest2manager mailbox) , guid for mail db is invalid. The event will be ignored.-------------------Also, Exchange message tracking shows me that this is a Submit StoreDriver event. The client type is: Transport and then it just says INVALID SENDER.I think this is where getting the info to the delegate break. HELP.EnaLd

Thanks so much for replying. I'll will post at the Exchange forum.