User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:72.0) Gecko/20100101 Firefox/72.0

Steps to reproduce:

68.4.2 There are some actions that cause TB to not be able to connect to the current network connection. Change the network by closing Wi-Fi and enabling Ethernet. Start up a VPN after TB has started up. Unplug the Ethernet connection, thereby changing to a Wi-Fi connection, if available or vice versa. Plug the Ethernet connection back in after disconnecting the cable.

Actual results:

In those situations, TB can no longer make an outside connection to the mail servers (any of them). It is necessary, then, to Quit TB and restart. Often it is the "startup" applications that conflict with one another. Example, TB starts quickly, VPN starts a bit later. Result is that TB cannot connect to the outside world. TB reports that it is unable to connect, or a "timeout" occurs, etc.

Expected results:

Any change in the network should be sensed by TB and not assume that there is only one available connection. TB should then "find" the available connection and use it. The same happens in Firefox (I will report same feature request in that forum).

In my opinion this is a bug and not a feature request. It exists both on Windows and MacOS. Can this ticket be changed to a bug report?

Is there some reason you can't take Thunderbird offline using the icon in the status bar or the File > Offline > Work Offline menu item before doing all this reconfiguring?

Then go back online after.

Does the issue still present itself using the currently supported 91.3.2 version? Version 68 is EOL and no longer supported.

That workaround would probaby work, but changes can happen anytime, for example when I'm at work and remove my laptop from a docking station and it connects over WiFi instead of Ethernet, or when I have to connect to a different location through a VPN.

This happens in the latest version (91.3.2).

I don't think I have seen this.

Antony, m_kato, can you reproduce?

I can reproduce this easily - it happens very often since I must now disconnect my VPN for certain other needs (certain web sites will not permit a VPN connection, etc.). All I need to do is to start up the system with VPN, start TB and other applications and use, then disconnect VPN in order to access a "particular" web site. TB is now unable to check for mail - timeout or other connection error. Workaround (as I have experienced) is to quit TB and restart. Using 91.7.0 (64-bit) now on Mac.

Gecko provides nsINetworkLinkService to detect network connection, but comm-central won't check whether network is online/offline automatically using it. So I guess that this will occur, but I think that this is a kind of feature request.

So, as I understand it, the workaround is to take TB off-line, then change network connections, then bring TB back on-line. Did I get that right? Thx.

(In reply to mark from comment #8)

So, as I understand it, the workaround is to take TB off-line, then change network connections, then bring TB back on-line. Did I get that right? Thx.

I did myself encountered such issue with TB when using vpn especially in work environent where IP of mail server (or other intranet services) change due to vpn connection to an internal ip (traffic routed via vpn) vs external IP (direct Internet access).

Upon network interface change events (such as connection/disconnection), I noticed that putting TB offline and back online never sorted the issue because it does not clear/update/invalifate TB internal DNS cache, nor ipconfig /flushdna on Windows does (because TB uses its own cache mechanism, it seems), nor clearing TB cache.

Workarounds always been to exit TB and restart it or wait for TTL to expire (internal IP TTL set to 5mn to reduce inconvenience) but none of those are ideal. TB should be able to detect changes in network connectivity and "adapt" automatically to the environnent.

This issue has already been reported but never been fixed. I am glad to see it is reported here and that there is now a glimpse of explanation about the possible cause. My view on the matter is that it should be considered as a bug not as a feature request ;-)

(In reply to Wayne Mery (:wsmwk) from comment #5)

I don't think I have seen this.

Antony, m_kato, can you reproduce?

I'll have a go a bit later and report - me also (AdP)

Is the bug around the use of a VPN only or in the main, or just one aspect?

Or is it mainly caused by switching networks between WiFi/Ethernet?

I do not use VPN as a rule, but switching networks does not cause TB to stop connecting to the server, I was switching whilst TB was still on-line

Ah, I now find that I have reporduced this oissue, I had to restart TB to get new emails. Off/On-line switching was not enough