Been doing lots of searching and reading on this issue but this Error 1506 seems to me to be pretty useless.
I have a solution where FMS needs to automatically send out notifications for Membership expirations. It worked in testing but then I started getting the odd 1506. I was capturing the error, but wasn't doing anything with it as it was all happening server side and I needed the process to continue. To monitor what was happening I added a Email Log/Queue such that second server side process could try again for any entries with an error code 1506. Most message go out on first attempt. In general those which failed with a 1506 will go on the 2nd attempt. Now I'm finding that some messages are actually being sent even though I'm getting a 1506. This is really annoying as the recipient is getting multiple copies of the same message and FMS just keeps sending them as its recording a 1506 error. I have been forced to put a max attempts filter into the Queue such that it doesn't go on forever.
Its got nothing to do with the format of the address fields. I've followed the advice and they only contain the address.
Why does FMS record an error 1506 when the message was actually accepted for delivery?
It seems to me that the most common 1506 situation is where there is only 1 message in the queue. The email server may be responding in a particular way on the first SMTP connection. The message is in fact accepted by the response confuses FMS and hence it reports a 1506. Some 30 minutes later the Email Queue process trys again and gets the same response, so the message is sent, but FMS records a 1506 so it stays in the Queue for further attempts.
The most recent example was last Sunday morning when 2 message were added to the Queue at 8:00am ... I'm a recipient. This has been working for weeks without any changes to the addressees. One of the messages went, the other got a 1506. I received copies of that "stuck" message every 30 minutes until 3:16pm when FMS finally recorded Error = 0 and the message was finally tagged as "Sent" The Log/Queue has incremented the Attempts count so it was the Error 1506 which caused the multiple deliveries ... it wasn't the local Exchange server.
Is it possible to get FMS to provide details of why its generating a 1506? Clearly the message is being accepted for delivery and it is in fact being delivered, but there is more to the story.