I’ve run into this a few times now, and wanted to share more details on this issue. The scenario in which this occurs is perhaps not quite so common, but then again, depending on how you have folks with Delegates set up, it could have more of an impact on your organization.
In a scenario where there are multiple Exchange organizations (or multiple connected organizations, such as in a Notes –> Exchange co-existance scenario), and the delegate of one person sends a meeting request to someone in the other organization who also happens to have a delegate, and the delegate is configured to receive the meeting requests, the meeting request may not be delivered to the delegate.
Let me see if I can simplify this with a diagram.
This problem is seen because when a Delegate sends the meeting request, the Sent-By field is populated, and this field is what is used for the Sender address. Unfortunately, this field gets populated as “SMTP:mailto:user@organizationA.com.”. This is a problem because anything after the SMTP: is interpreted as the address, and when the mailto: is present, that is picked up as part of the address. Colons are invalid characters in an smtp address, however, so when the message is processed, an invalid sender exception is thrown, and the message does not get delivered to the Delegate.
Another side effect of this issue was that the “Messages queued for submission” performance counter would be incremented on the destination mailbox server, and if you have a monitoring solution in place (such as Microsoft Operations Manager, or System Center Operations Manager), alerts may be generated. More information about this can be found in KB article 953094
The good news is that this was fixed in Rollup 7 for Exchange 2007 SP1 (and would thus be included in both Rollup 8 and 9 and beyond since Rollups are cumulative), so unless you are behind on your rollups, hopefully you won’t encounter this situation. It’s also worth noting that the fix (which works by simply stripping out the mailto: portion) needs to go on Hub Transport servers. So make sure that your Hub Transport servers are running Rollup 7 or higher!