SPAM messages deleted in Thunderbird remain server-side in the SPAM folder

[tangodev]

Removing SPAM is not reliable.

Expected Behavior

When clearing SPAM in Thunderbird, the change should get replicated and seen in the Webmail.

Current Behavior

When clearing SPAM in Thunderbird, the messages are left in the SPAM folder in Webmail.

Possible Solution

This seems to be tied with this:

1. Messages moved to Local Folders in Thunderbird stay behind in Webmail #434
2. Drafts made in Thunderbird are not being deleted server-side after being sent #433
3. Mozilla Thunderbird - Retention Policies - Mail expired from normal folder still exists in 'All Mail' and in webmail 'All Mail' #386

Steps to Reproduce

1. In Thunderbird make sure you have some messages in SPAM (you can drag some in for the sake of the test)
2. RMB on SPAM and select Empty Junk
3. Confirm
4. Wait for sync
5. Messages got deleted in Thunderbird but not in the Webmail

Version Information

OS: Kubuntu 23.04
Thunderbird: 1:115.3.1+build1-0ubuntu0.23.04.1
Bridge: v3.4.2 (br-165)

Context (Environment)

Removing things from SPAM is a basic thing that should Just Work™️, esp. given how much spam some users tend to get. Once purged, the messages should be removed everywhere to avoid duplication of work.