Hello, I have an em Client version 7.1.30794.0. My organization switched to Office365 recently, and since that I get this error: “synchronizing folder list failed due to the following error: The remote server returned an error: (404) Not found”, every 10 min. Emails are received and sent without problems, calendar and offline address book seems ok too. I try to delete all OAB files from user/AppData/Roaming/eM Client , but it didn’t help. Any suggestions? 
One thing you could try is to delete the account in eM Client and add it again.
Always make a backup before deleting accounts, just in case.
Actually I’ve done this a few times, with the same result (404 ,Not Found, etc). I think this situation is related to the path (for remote folders, calendar, or address book) somewhere in settings, like outlook.office.com or outlook.office365.com/.../…, which as I understand should be set automatically during em Client set up for the Exchange server, but somehow was not set correctly. I try to change these address settings (they are different for remote folders, calendar, and address book) by myself, but the problem still persists. Or may be it’s a timeout problem, I don’t really know how to check it from the log file.
I would contact your Exchanger server admin and ask for assistance.
Well, our admin doesn’t know much about eM Client, I asked him first of course. Mostly because people use MS Outlook, which (in this case at least) was working without problems.
Because the error appears to be an Exchange server error, one would hope that the server admin would be able to give some assistance.
I am having this problem as well. I’m running latest version of eM Client in Windows 10. I have it configured with a Google account (G Suite) and an Office 365 account. There is nothing special about the Office 365 / Exchange setup. I just used the auto config. I am getting the same exact error as the original post. It happens every time I launch eM Client. I just close the box and go about my business but it is very annoying.
Hello Kenny,
Please try the manual Exchange account setting instead of the automatic setup in Menu > Tools > Accounts > Add account > Mail > Exchange. Please let me know if it helped.
Russel
I want to let you know that I tried adding the account manually as an Exchange account. I still get the error box to come up. It usually happens when eM Client is left open for a while. Exiting Em Client and re-opening fixes the problem.
Just checking to see if you have come up with any fixes to the problem. It seems that when Em Client is kept open for long periods of time – the error notifications box always comes up with a mention of the Office 365 / Exchange email account. This is unacceptable.