some mail sites (for example, yandex.mail) store deleted emails for 30 days on their servers.
#₽ Suggestion:
Before permanently deleting a message, mark it as “spam”. Spam emails are stored for 10 days, while regular deleted emails are stored for 30 days.
I think this might have a very bad side-effect: Chatmail servers would be blacklisted for apparently sending lots of spam. Then messasges from them would be blocked.
Have you tested if this is really the case with delta chat or is this just a theory at this point?
Deletion in other email clients and in webmail is normally not delete but “move to trash imap folder”, but delta chat tries to really delete emails, not just move them to trash folder.
Could be that the server/provider in question handles IMAP deletion action differently, so would be good to know (for this discussion) if you confirmed that those providers really keep emails that were deleted from delta chat.