Comment 48 for bug 885525

(A) Reason why I proposed new mail.server.serverN.force_Gmail_Trash_if_is_gmail in comment #40.

Usage of is_gmail I showed in comment #44 is similar to useCondStore - user can override "CONDSTORE returned in CAPABILITY response" by useCondStore=false in prefs.js.
However, isGMailServer/is_gmail is also used for getting X-GM-MSGID, X-GM-THRID, X-GM-LABELS from Gmail IMAP. So, "override by is_gmail=false" can't be used for disabling "Forcing [Gmail]/Trash".

(B) Reason why I proposed simple "new mail.server.serverN.force_Gmail_Trash_if_is_gmail" and "small logic change in nsImapIncomingServer::DiscoveryDone()" in comment #40.

Current trash selection UI at Server Settings has some big problems:
  - Isn't torelant with localized folder name in localized Tb.
  - Isn't torelant with namespace.
  - Isn't torelant with "IMAP Server Directory:" and it's change by user.
And, similar folder selection UI to Copies&Folders and Junk Settings, which automatically resolves above problems, is already proposed.
So, correct UI enhancement such as "use folder in XLIST" should be consistent with other UI changes and should be consolidated to other UI changes.
And, there is already known problem in Copies&Folders and Junk Settings when XLIST or LIST(EXTENDED) is used : bug 800035.
Further, workload of big UI change is not so small, and it usually takes long.