Neal,

1) This is a known issue with Outlook and the non-supported EAS protocol. In a one-on-one screen share session with Microsoft, I was able to show to them that Outlook is only sending one message UID in the delete command instead of the several messages that are selected.  The server only receives that one message and will delete it.  Outlook, however, will react as if all of the messages were successfully deleted.  Microsoft's response (like so many times beforehand) is that ActiveSync is NOT a supported protocol for use with Microsoft Outlook.

2) I will review this further, however, all of our local devices and accounts seem to be getting the notifications just fine.  One question for you?  Do you have your SmarterMail app pool configured to recycle on a daily basis.  We have had other very large customers start to do that and their EAS performance has increased.  We are looking into way recycling often seems to improve the behavior.

I hope this helps.  Thanks.

Re: 1 - that's disturbing, I've grown to just hate Outlook. Win10 mail using EAS doesn't have this issue but it doesn't sync on delete but instead batches, i.e. does timed sync cycles it appears. Mac mail is just better but I'm trying to get my world back on Windows as a developer...oh well, maybe I need to just fall back to good ole IMAP

Re: 2 - I restarted the service this morning prior to my post and so far it's working again. I have not heard of setting a recycle pattern for IIS. I purged all deleted, sent, archived, junk email folders to try to help any synchronization especially with new account setup/testing so it's not that large of a user account.

Will continue to monitor. 

Neal,

RE: 1 - If you go into the account settings and change the download new content setting it should help with the "batching" you are seeing.  By default WinMail uses "Based on my usage".  Change this to "As items arrive".  Personally, I use WinMail as my preferred client.

RE: 2 - In IIS, you can select your SmarterMail application pool, click on Recycling... from the Edit Application Pool options on the right.  In the popup modal, You can specify conditions for when to recycle the app pool.  We have found--and suggested to other clients with large customer bases--to recycle the app pool during a period of least usage.  For us, 2 AM every morning works.

Thank you, I use the same settings as you described above but I think for deletions they don't delete from the server right away, I'd have to retest this. 

I'm not sure the recycling will help but I can try it. Restarting the Windows Service seem to resolve my issue which means something like a memory leak or something internal to the code was hanging up. I'll setup IIS recycling now and see how that works out.

Edit: I set it up but the default recycling is 1740 minutes (29 hours) so IIS auto recycles the app pool unless you configure it otherwise.

We had to setup recycling otherwise clients would complain that Outlook stopped syncing for EAS. Once we setup a recycle, we havent really had any complaints. Though I do wonder why IIS has to be recycled nightly, surely in 2019, IIS can run an app longer than 24 hours without needing a recycle.

What is IIS pool recycling ? Is it something like needing to restart regularly your php-fpm pool because a poorly coded app is rendering it unstable after a few hours of usage ?

Yes, it basically destroys the running w3wp.exe worker and spawns a new one. Frees up resources etc. Think of it like rebooting the IIS application :)