Just my 2 cents about EAS on SM16 after using v16 for the last 6 months through good and bad times with multiple users that have mostly 1GB - 5GB mailboxes, but also 10GB+ 15GB+ and 50GB+ mailboxes:
- Overall ActiveSync is much better in v16 than v15 - in 15 it was horrible with all possible issues
- The larger the mailbox, the more issues
- If you are using Outlook 2013/2016 with EAS, waiting for it to sync your whole mailbox (do not trust it when it says "All folders up to date" - it will say that as soon as it has synced the Inbox and Sent folders) will solve most of the issues
- generally syncing contacts and calendar works quite OK
- syncing tasks works nicely
- EAS with modern mobile devices (tested mostly with the mobile Outlook app) works quite good if you only sync Inbox / Sent + 1-2 other folders and in total you have less than ~ 5000 emails. Above that number, multiple users experiences intermittent issues that were only resolved if users synced less folders or reduced the no. of emails in Inbox by moving them to another folder that is not synced all the time. Other than that, generally when you flag an email, you mark it read/unread, you move it to a folder, etc - that action will be performed on the server in a short time.
- If you have a large mailbox and Outlook did not sync it all, then:
>>> you might mark a mail as read and it will show up as unread at the next sync
>>> emails will show duplicate contacts
>>> you move an email to a folder and it might get duplicated: you`ll get one in Inbox and one in the folder you moved it to
>>> you will try to flag an email and the flag will disappear at the next sync
>>> Outlook will take a lot to send your changes to the server, meaning that if you work exclusively with Outlook during the time that it is still doing the initial sync (and with ~10 GB mailboxes it will take more than a week to fully sync), if you log in the WebMail after a few days you`ll see you have a lot of mails that were not moved to folders, that were not flagged, that were not marked as read, etc. Totally untrustworthy during the initial sync.
>>> if you create a new folder or subfolder, it is very likely that it will not also be created on the server and if you move emails from Inbox to the newly created folder you just moved them to a black hole and it`s not certain if you will ever see those emails again :)
- Now, if you did wait for Outlook to complete the initial sync (remember it will take more than a week for 10GB+ mailboxes), then:
>>> any action you make in Outlook (mark as read, flag, move email, etc) will take at least a minute to sync to the server, but it will sync quite reliably and it usually takes less than 5-10 minutes, depending on how many actions you take at once. So with Outlook there is always a small delay.
>>> flag/remove flag actions work 100% of the time
>>> mark as read/unread actions work 98% of the time. Literally we`ve seen that out of about 100 emails marked as read, 1, max 2 will stay unread in WebMail afterwards..
>>> move actions also work ~ 95-99% of the time.
>>> creating a folder: really tricky - we`ve recommended users to always create/move/rename folders from WebMail, as if they do so in Outlook, the bigger the mailbox the higher the chance that the folder will not be created on the server.
Bottom-line: EAS for us was a really rough ride though hell, but nevertheless it was a necessary one: there was no alternative for also syncing calendar, contacts and tasks along with mail though one single login.. even with all of the issues.
> Mobile users have almost no complaints at all, except those with huge mailboxes and who want to sync them all
> Most Outlook 2016 users also have no complaints as long as they have mailboxes less than 10 GB and respect an internal guide of managing their mailbox (creating folders and subfolders under the Root - never under Inbox, Sent, Deleted folders and then make sure to keep email count lower than 5000 in any one folder)
Really, now the only complaints come from the users with very large mailboxes and those that just set up Outlook again (already have a decent sized mailbox) and find that all sorts of Poltergeist events occur until the mailbox is fully synced. For example, for one user that had the mailbox go over 60GB, we`ve had to create a second account and move some long unused mails to that one so that Outlook would be usable again.
Since we`ve had so much trouble, we`ve also watched threads with similar problems reported to Microsoft and for other software that have EAS and SmarterMail is definitely not the only ones affected. Overall I would definitely say that the EAS protocol is designed wrong and its implementation in Outlook brings about even more issues - so many that Microsoft just decided to drop it.