IMAP means synchronizing the mails, no way around it, that’s the main point of using IMAP.

In order to provide this kind of flexibility and functionality, though, messages must be synchronized between the local machine and the email server.' Full-text search of a message body is only possible on messages that have been downloaded. Search performance is much faster than searching a set of messages on a remote server. Messages load faster when they are stored on a local drive. Thunderbird users can download their messages to their local system and access them even when they are not connected to the internet. For example, a Thunderbird user with a Microsoft Live account can use both the Thunderbird application that is installed on their system and the web-based interface provided by Microsoft. Multiple clients can be used to access messages. Therefore, messages can be stored both on the local machine and on the server, enabling numerous benefits: The IMAP protocol supports both online and offline activity. On Thunderbird you get all your messages to work offline don’t you? NB : I have a Mac, so Thunderbird is the Mac version. This is very annoying so if it happened to some of you too, and you have the solution, I will be very grateful!! It seems this happens also to some other persons, but on the forums nobody found an answer. I searched on Thunderbird support, nothing. However I noticed that once I delete emails on the server, they automatically disappear also on Thunderbird !! Though normally the advantage with IMAP is that everything should remain in Thunderbird… I already checked all the sync options, I ticked and re-ticked “keep all messages in Thunderbird inbox” etc. Normally, as everyone explained to me here, with the IMAP connexion my emails remain on Thunderbird, and I got to manually delete them on the server - which is quite easy and useful, since my Inbox on Riseup is very limited. I use a riseup account, with an IMAP connection, to be able to get my messages on both interfaces : my FP through K9 Mail and my laptop through Thunderbird. If anyone has the solution, please help me !

I got a problem with my email synchronisation… I tried to find an answer everywhere on the web but I never found how to deal with it, so this is my last chance here.

K9 mail download