EAS Emails suddenly disappeared from Outlook 2016
Problem reported by Cristina Precup - April 12 at 7:05 AM
A client of ours that uses Activesync opened Outlook today and all her emails suddenly disappeared (they didn't disappear from the server or from her phone though). She had approx. 24 GB of emails. She said that she didn't do anything, she just opened Outlook and it looked like it was frozen and then it started deleting all her emails. That happened with all her folders and she has many. Then she reopened Outlook and it started downloading all her emails again (but it still hasn't finished because she has thousands and it might take a few days). What could have caused this? It's pretty strange and really inconvenient.
Thank you

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Information Technology Replied
Hi Cristina,
There are some limitations for EAS on desktop applications.
For your desktop, if you have a large mailbox, OVER 5,000 messages or 5GB of space used, IMAP is the protocol you should use for your email. For your calendars or contacts you can use any other of the sync protocols (such as CalDAV and CardDAV) but for your email, you should use IMAP. IMAP has push-like support with the IMAP IDLE process, which pushes new messages to your desktop client at a set interval.
MAPI over HTTP is suppose to be an option in Smartermail v17 which is currently in Beta. I haven't reviewed the release notes to see if it is there yet. This is a solution exclusively for Outlook 2013+.
And do note that there is a documented issue when adding EAS accounts in Outlook 2016 after Microsoft Update KB4011091. You would need to install or rollback Outlook 2016 to a version before (16.0.8326.2096).
Probably not the answer you were hoping for but I hope it helps. Have a great day.
Information Technology Replied
I just saw a post on the blog about a workaround for the EAS account creation issue. I wanted to add it here just to be thorough.

Microsoft Support published an article "How to disable Simplified Account Creation in Outlook 2016" on 9th September 2017 which provides the registry entry to enable the traditional account dialog box to configure new accounts in Outlook 2016. What confused me was the the subkey in the registey (HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\setup) does not exist. However copy the following 4 lines into notepad:

Windows Registry Editor Version 5.00


then save/rename it to "disableoutlook16simplifiedaccountscreation.reg". right click the entry and select [Merge].
The usual warnings apply to altering the registry - back it up before doing this.

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