We also have some MAPI customers reporting this. The only workaround we found right now is to tell them to click on "Update folder" (on the same bar as send/receive which does nothing at all).

For most of the user, the "Update folder" button triggers the new messages arrival.

As I was able to duplicate the issue with a fresh account I monitored a bit what's going by sniffing Outlook traffic with fiddler.

I don't know if this is linked or not but everytime a new message is coming in, there is a call to an external URL (on microsoft network) (a roaming stuff url)

(copy the image to clipboard to see it full screen)

When the message aren't coming as they should, I can't see this call in fiddler.

While googling around about the issue, I saw that other people had the same issue but with their mails being hosted at office 365, so I wonder if this is somehow linked as it seems Outlook is calling "home" even with on promise setup.

Hello, 

Thanks for posting to the community. I would recommend giving this a shot. 

Please let me know if this helps. 

Kind Regards, 

@Zach, we've been using this patch for a while and it helps speed up autodiscover during the initial profile setup.  But what my original post dealt with is long delays receiving new messages on MAPI clients already set up (after running the .reg patch before adding the profile).

Clicking the Update Folder button per Sebastian's post does help fill in the missing messages, but obviously something is wrong because user's should not have to manually click a button to get new messages.  

To be clear, this is not all the time.  Affected users sometimes have fast and reliable new-message arrival.  But they will be working actively, hearing their mobile device ding with new messages when Outlook does not receive anything until hitting Update Folder.

Also, there will often be gaps.  I did a screen sharing with one user who had emails from all morning up to about 1:00 p.m.  Then there was a gap from 1:00 to around 3:00.  Then around 3:00 there were messages to the end of the day.  In order to pick up that missing 2 hours, he had to click Update Folder.  This user had been working continuously with Outlook running during the 1:00 - 3:00 gap.  Outlook just hadn't received anything, even though there were over a dozen messages from 1:00-3:00 that were visible in webmail and mobile device.
 

@Jay

Thanks for the follow-up. I see what you mean. I was thinking that this might prevent Outlook from reaching out to Microsoft. In the past, I had a client who was having a similar issue, and what ended up fixing it was just resyncing. After this, the user didn't report the problem again. We have a new resync user protocols button. So maybe this would be worth a try?

Please let me know your results. 

Kind Regards, 

@Zach

Unfortunately, been there, done that both ways.

We've completely deleted and scrubbed the profile, then started fresh.  Still occasional gaps.

We initiated the sync from the server/admin side.  Still occasional gaps.

We even tried the old trick of disabled power-saving on all NICs to prevent them from going to sleep during inactivity also, but that had no effect.  This wasn't likely the problem anyway, because it also happens while users are actively working during the day and their computers are not sitting idle.

It's only a small subset of users, but understandably problematic for those it affects (including a C-suite executive of a very large company).