First thanks to @Paris Geek, @mikeone and @SrT for the active discussion; it is appreciated. As most will agree constructive dialog usually yields the best outcomes provide emotions are kept in check (note to self) and sacred cows remain in pasture.
re: "I consider your request as not needed (cf. my suggestion you're rejecting) and dangerous for other users:
One day, a user would unselect by inadvertance this option, then his Deleted folder will not get synced, and problems would appear. He'll put 1 star on Google play, and say that Aquamail is broken. Unfortunately this is real life."re: In my opinion "... the danger" could be as follows:
The user deleted a message (removed from the inbox or from any other folder, moved to the deleted folder). Afterwards he need the content of this deleted message on another client. Unfortunately this message will be only available in AquaMail, but not on any other device (mobile or pc or even in the webmail account) ... since it was not synced back by AquaMail to the servers deleted folder.
This situation could be very annoying.I had considered this but felt most would understand their choices (especially if overtly changed from default values) and recognize what had happen just like with any other selective sync. In that regard I don't see operations on the
deleted folder being any different than
spam but also realize everyone might not see it that way.
re: In this specific case - if you are not going to look at those deleted messages (ever) - why not using AquaMail's action "Delete now" (remove deleted messages permanently from server)? That's how I'm dealing with those useless messages.I do use this and can confirm it works for Gmail. However, given high mail volumes it is not efficient to decide between a 'normal' delete and 'immediate' delete while processing each message. Peforming this action in bulk from the deleted folder in AquaMail leads to long sync times (seconds to minutes) on fast connections - likely due to limitations in the protocol which mandate each message be handled individually.
I am looking into a way to more efficiently cull messages on the server side using a combination of AquaMail and the GMail
mobile interface which retains 'delete forever' capability on multiple messages. Current challenge is multi-select in Gmail as each item must be ticked individually. The GMail app supports multi-select but, like most clients, downloads messages rather than acting directly on the server version.
There seems to be a lot of energy around this request so I will withdraw it (again). Bit of a head-scratcher as the same selective sync choice exists for
spam. Obviously misread the tea-leaves.