[Dovecot] Idea: POP3 deletion as a flag

[Timo Sirainen]

GMail doesn't delete mails when POP3 client issues a DELE command for it. Instead they just become invisible for future POP3 sessions, but they still exist for IMAP/webmail. The same could be implemented pretty easily for Dovecot:

 - Add a new setting to enable this: pop3_deleted_flag = $POP3Deleted
 - When DELEting a message, add this flag to the message.
 - When listing messages, skip all messages that have this flag.
 - Also hide this flag from IMAP clients(?)

Thoughts? Probably 20 lines of new code.