Opening up a ticket will be the best solution for us to troubleshoot the problem.

I did that and working with support now.

Just posted in the forum to see if this is a known problem.

Try not to waste support help if its already known.

Thanks.

Follow up.

I did setup the same account on a different device using both mapi and Imap, also using Outlook 365.

The mapi account did the same thing, missing emails that’s on the server.

Imap had the missing emails.

 

So MAPI is not working with the account, found 2 more accounts with the same issue.

This is happening with me also. Confirmed today. I am having to delete .ost file and resync MAPI account.

Seph,

I deleted the account, basically followed the steps from Smartertools on how to remove the account but same issue occurred after that.

Only noticed this in Outlook 365, which version did you experience this on?

Please open up a support ticket on this.  I know its the same issue that was originally reported but the cause could be very different.  

@Heimir Eidskrem - Outlook 2016 - so far

Seph,

Got another device its happening to now.

Also got this regarding the same account.  Have you seen anything like this?

"Ethan gets emails from us, but is not getting emails from Jimmy (for example).  And if he gets an email from an outside source where Jimmy is copied, when he tries to reply to all, he gets a message about the user not being found.  He has to delete jimmy’s address and then retype it and it will go."  

Only seems to be with email from other users in the same domain.

@Heimir Eidskrem

I had pieces of that problem. For a while, names would not resolve with email address that is in Contacts on the server side. I would check if there are any characters in the display name of the user besides letters. There was an issue with ampersand [&] in the past - look for any apostrophes - anything besides letters and numbers.Does "Jimmy" appear in the Global Contacts in webmail? These are the starting points I would look at. It might be that you have to delete the .ost file and then delete the "sync" file in their account and re-sync again. That is the best baseline to start with also for troubleshooting.

I think this is a server side issue and at this point we are moving the users back to IMAP.

Jimmy is in the GAL.

This problems does not exist in Imap as far as we know and switching them back resolves the problem.

And we have another account with the same problem.

So we are switching all users back to IMAP as a solution for now.

Got another request to switch today.

Its strange but after a while the MAPI accounts stops downloading emails for certain users in their own domain.

Seph,

Are you seeing the same?

IE, account works fine for a while then this behavior starts by not downloading all emails.