User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:84.0) Gecko/20100101 Firefox/84.0

Steps to reproduce:

Situation: you're going on a bus/train/etc trip with your laptop and you want to write some email replies in Thunderbird using it's offline mode. This is a defining feature of Thunderbird and one of the main reasons why you use it instead of webmail interfaces.

Procedure:
(1) Unplug or disable all internet connections on your computer
(2) Notice that Thunderbird's "offline mode" icon on the lower-left corner of the window (status-bar) has changed to say offline.
(3) Click this icon to actually put Thunderbird into offline mode
(4) Notice that the icon does not visually change.

This is very confusing. Clicking it again to take Thunderbird out of offline mode also doesn't change the icon (unless you now also have an internet connection again).

Expected results:

Previously: status of offline mode icon = offline mode status
Currently: status of offline mode icon = OR( offline mode status, network unavailable )

The original logic made sense: the icon only has two visual states (1 bit) and it only related to one feature (1 bit). You click it to change into or out of offline mode, its icon changes to show this.

The new logic is confusing: the icon still only has two visual states (1 bit), but it's trying to represent 2 bits of information. You have to guess as to what these bits are in 3 out of 4 cases. Most often: you click it and it does not change visually. You already know you're disconnected from the internet, that's why you want to click it.

Suggested solutions:
(1) Make the offline mode icon only refer to offline mode status (as it used to), not also a bitwise OR()ing with network unavailable.
or
(2) Split network unavailable into a separate icon/feature in the statusbar.

Bug appeared in a stable release some time (approximately) last year.

What Linux distribution are you using?

Most, except those supported by Canonical like Ubuntu, are up to date with at least version 78.6.0, while Ubuntu and it's derivatives are still at 68.10.0 which was EOL back in Sept. 2020.

I'll try a test with the 78.6.0 on my Fedora 33.

Apologies, I'm on 78.6.0 (not 68.7.0). Editing now. Thankyou for bringing that up, my mind is a bit backwards.

Answering you question: Void Linux x86_64 (a rolling release distro, typically packages upstream stable releases).

Regression of distro? Or regression of Thunderbird?

Sorry for returning late to this one.

This is what I see when following the reporters steps using version 78.9.1 on Fedora 33 Workstation, Gnome desktop.

I do not have any reason to assume this is a distro-specific bug, but I could be wrong.

@WaltS48: that is the icon. Traditionally it only changed to the red-slashed-through version for one reason (clicking it to enter "offline mode"). Does it also now appear with a red slash if you disconnect all internet connections to your computer?

[Sorry if this is all confusing, the terminology of "offline mode" versus "no internet connection" describe very different things in Thunderbird, despite them sounding the same.]

Thunderbird should detect your network status and change to offline mode when you have no network. I would suggest the reported behaviour is actually correct behaviour.

Despite bug 391732 still being open, I had thought this was the default for Thunderbird on all platforms and it does appear to be the case here https://searchfox.org/comm-central/source/mail/app/profile/all-thunderbird.js

Thunderbird is not changing to offline mode when you have no network. It is simply changing the appearance of the button when you have no internet connectivity, pretending to be in offline mode.

"offline mode" = a specific feature of Thunderbird that is toggled on and off manually (and perhaps automatically as you suggest, but I have not seen this yet). When this feature is enabled: the "Send" button on an email composition window changes to instead say "Send later", no autosaves of drafts to a server are attempted and several other small things change.

"having no internet access" = something Thunderbird detects.

The icon in the tray of Thunderbird used to indicate the status of offline mode. Now it instead indicates OR(offline_mode, having_no_internet_access).

I'm going to make a video to explain this bug, I think this is too confusing.

Offline/online mode is automatically detected. (But you can of course force it to offline for special use cases as well.)

This demo should help: http://halestrom.net/misc/otherforums/thunderbird_offline_bug.mkv

Note that the automatic detection of internet connectivity is different to the status of offline mode.

N.B. if automatically detecting internet connectivity did toggle offline mode automatically then we would have other issues, in the form of dialogs spamming the user if their internet connection is flapping. Offline mode (in its current form) is designed to be a manual feature, it would need reworking to be ergonomic as an automatic one.

(In reply to Hales from comment #6)

I do not have any reason to assume this is a distro-specific bug, but I could be wrong.

@WaltS48: that is the icon. Traditionally it only changed to the red-slashed-through version for one reason (clicking it to enter "offline mode"). Does it also now appear with a red slash if you disconnect all internet connections to your computer?

[Sorry if this is all confusing, the terminology of "offline mode" versus "no internet connection" describe very different things in Thunderbird, despite them sounding the same.]

I followed your steps starting with step 1.

Just tried it again and attempted to Get Messages, which failed because the application could not connect to the server.

09:41:38.195 2021-04-19 09:41:38 Feeds WARN downloadFeed: network connection unavailable

​

(In reply to WaltS48 [:walts48] from comment #11)

I followed your steps starting with step 1.

Just tried it again and attempted to Get Messages, which failed because the application could not connect to the server.

09:41:38.195 2021-04-19 09:41:38 Feeds WARN downloadFeed: network connection unavailable

Get Messages does not work when offline. That's normal. I don't think this is related to this bug.

Everyone reading: please see the short video I link above for a concise and clear explanation of the issue. http://halestrom.net/misc/otherforums/thunderbird_offline_bug.mkv

(In reply to Magnus Melin [:mkmelin] from comment #9)

Offline/online mode is automatically detected. (But you can of course force it to offline for special use cases as well.)

I disagree Magnus. I recently had an internet outage where the cable was out for a day. Thunderbird sat on the desk and tried to get mail all day. It never worked out it was connecting to oblivion. and the online offline indicator in the statusbar never changed state.