Our company has recently switched from Kerio Connect on-premises email server to Exchange Online. We had been using Thunderbird and had no problems previously.
After switching to Exchange, Thunderbird is intermittently throwing Connection Timeout errors. Because multiple users can be sharing an inbox, this causes a great deal of confusion because once the connection times out, the inbox is no longer the same as the other users and they do a lot of moving emails and renaming the subject (using header tools). I am using OAUTH2 for authentication. The timeout might happen a few times a day for each user and it sometimes only lasts for a few seconds and they are back in again. Sometimes it lasts for a few minutes. There is also a user at a different site which it occurs for as well.
I have tried:
- Ignoring Thunderbird process and folders in Windows Defender Antivirus.
- Increasing the timeout in Thunderbird (mailnews.tcptimeout)
- Reinstalling Accounts
- Updating Thunderbird to the latest version.
- Updating Windows.
It doesn't seem to happen to all users at the same time even though they are sitting next to each other.
It is the first time using Office365 so I am not used to it, but I can't find anywhere in there to diagnose failed connections, etc.
Does anyone know how I can get to the bottom of this issue?
Further Info based on Rohit Gupta's reply:
- We are using IMAP.
- All users are on Windows 10.
- Different users get the error message intermittently, but not all at the same time.
- The account is a shared mailbox with 6 users
- I found the sign-in history in Azure AD and there is no log for when the connection timed out.
Further Info based on Geeky51's reply:
- Some users are working from and have a different IP address and it happens for them intermittently too.
