i'm facing a problem on my mail server. I'd one mail server which was running on postfix+dovecot. due to some problem I reinstalled the server with all the services after taking backup. now when it is working i want to restore the mails of all the users. problem is if i restore all the mails to respective mailboxes all the users will get all the old mails too which they have already downloaded. now i want users to download only new mails and the mails which were never downloaded after restoring the old data. is it possible? I tried by deleting dovecot.index and dovecot.index.cache files from one mailbox on test basis. it works but dovecot rebuilts the index files and allows to download all the mails which i put after deleting the index files. so is it possible to merge dovecot.index and dovecot.index.cache files any ways?????

once i had quite similar issue and in that case first i set up all mail clients (i was using thunderbird on almost all desktops) to not to keep a copy of the mails and then all the mails currently in the thunderbird was marked as read.

then downloaded all the mails and sorted by read status. then all the newly opened mails are shown as not read. after that i manually deleted previously received mails.

now this is a more tedious method. but i had no other option at that time.