SendLater ignores IMAP flags

[guest4711]

Prerequisites

• I am reporting a problem, not asking a question (for questions, go to Discussions).
• I have consulted the user guide.
• I have confirmed that I'm running the current version and the problem persists there (note the version number in fine print next to the add-on name on addons.thunderbird.net and compare it to the version number listed in the add-on details opened from the Add-ons page in Thunderbird; if you've got an old version, click the gear icon and select "Check for Updates").
• If I'm having an issue with date-parsing confusion, I've read the section about that in the user guide and I still think this is something different.
• If I'm having an issue with messages not being delivered, I've followed the troubleshooting steps in the user guide and it's still an issue.

Describe the bug

When deleted mails are simply marked as deleted (and not moved away), SendLater tries to deliver the mail again and complains the mail has already been delivered...

It simply fails to respect the imap "deleted" flag ...

How to reproduce

1. Open Account Settings -> Server Settings
2. Point to "When I delete a message" and mark "just mark it as deleted"
3. Create a testmail and let SendLater handle it
4. SendLater will send the message and delete the draft afterwards
5. Enjoy the popups of errormessages until you'll compress the draft folder (what will expunge the folder).

Expected behavior

Simply send the message, Do not complain...

Additional context

No response

Operating System

OS independend

Operating System Version

No response

Thunderbird version

115 - but probably version independend

Send Later start-up string

Send Later version 10.3.5 on Thunderbird 115.5.1 (20231128200102) [linux x86-64] UI locale en-US, Date Locale en-DK static.js:146:28

[jikamens]

@zephyrus9MA is having this issue as noted over in #605.

[jikamens]

I am prevented from fixing this by the Thunderbird add-on APIs. See https://bugzilla.mozilla.org/show_bug.cgi?id=1881929 . Until that is fixed the "just mark it as deleted" Thunderbird setting will be incompatible with Send Later.