Bugzilla

Rather than relying on the reference to the Send Later issue, I want to spell out in detail here what the issue is.

TB has a concept of automatically detected offline mode, and it knows to ask the user whether to send unsent messages when there are messages in the Outbox and TB transitions from offline to online.

The problem is that offline -> online trigger doesn't happen if TB is connected to the internet fine but only some of the servers it talks to are unreachable.

Specifically, if the user has an account configured in TB whose servers can only be accessed over a VPN, and the user starts up TB when the VPN isn't connected, and then connects the VPN, TB won't treat that as an offline -> online event.
I'm _guessing_, but do not know for certain, that this may only occur when the user has multiple accounts configured in TB and some of them are accessible without the VPN. This guess is based on the suspicion that TB's "detect when offline automatically" functionality is based on connections to mail server, and it thinks it's online if any connections are active. Just a guess, though, haven't looked at the code.
I'm not sure what the right fix is here. TB probably shouldn't run in offline mode if some servers are accessible, since that would block access to all servers.

Thinking outside the box, maybe offline vs. online is the wrong paradigm entirely for determining when to prompt the user about sending unsent messages. Maybe TB should be periodically checking not for offline vs. online, but rather for if any of the SMTP servers required to deliver messages currently in the Outbox were previously inaccessible and have suddenly become accessible, and prompt the user about sending unsent messages at that point.