We`ve also seen this, but just for a handful of accounts out of 200+. However, for us, just the Inbox starts re-syncing randomly - the rest of the folders are OK and retain the email. Usually our users have between 2000 - 10000 mails in Inbox. All of these cases are with MS Outlook 2016/2019 syncing over EAS.

For one user, this also happens on his mobile device - also syncing over EAS. He has more than 25000 emails in his Inbox. 

We are having the same issue just recently started.  I have opened a ticket with SM to see if they can find out the issue. 

WE have alot of complains with this problem.

You guys should all probably clarify what version of SmarterMail you're using.  I'm assuming this is in reference to the latest Beta update?

Latest stable build. 

I want to add some of my users to this problem. in addition, one users mailbox was completely corrupted just before christmas and required me to recreate and rebuild from backup. He is still having a problem with his sent mail and sub folders disappearing and re-appearing as well as other folders. He has about 3.7gb in his mailbox and using outlook 2016 and current stable build (non beta)

We've seen this from time to time. Support at Smarter Mail can't replicate and it dies there. Strange.

As a developer, I see it as the opposite. Until a developer can have a repeatable process you can't solve the problem. When a problem is found and repeatable it will be fixed. Not defending ST but maybe the fix isn't as easy as we wish it were and could take a couple of revisions to get the "fix in". Often the easiest to see problems are the hardest to fix.

We've had this problem with EAS and Outlook for the last few years on email accounts over 50K emails. We always have the latest stable build installed. I've tried every version of Outlook that supports EAS...up to Outlook 2019 and latest office 365 Outlook (pretty much same thing)... and all have the same issue. One common factor is that this only happens on laptops where i'm disconnecting and reconnecting to a wireless network. Sometimes it occurs again after major updates to SmarterMail...but once again only on my laptops. It has never happened on my desktop PC's. I've had this happen on 3 accounts with all the same characteristics. It happens more frequently when i change wireless networks I'm connecting to (i.e. when traveling or on a client site). I've tried it on 8-10 different laptops with the same issue and 3-4 different desktops with no issue.

I have a desktop computer, and time to time my outlook resync all email. I dont know how to reproduce the problem. The only way that I know that have a similar effect is make a significant change in webmail (or phone) with the outlook closed, and when you open the outlook, because the change is a little big change, outlook re-sync all the emails. 

We also see that the issue seems to be when connecting or reconnecting to a wireless network. I've figured it has something to do with a request / response getting interrupted and then the whole process starts over. It's hard to replicate since not clear when the connection gets lost. But interesting to hear it happens to others.