Problem with Thunderbird/K9 Mail IMAP sync

Hello to all !
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. If anyone has the solution, please help me ! :cry:
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.
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.
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. I searched on Thunderbird support, nothing. It seems this happens also to some other persons, but on the forums nobody found an answer.

This is very annoying so if it happened to some of you too, and you have the solution, I will be very grateful!!
Thanks a lot…
NB : I have a Mac, so Thunderbird is the Mac version.

I think the reason you have problems finding an answer to your “problem” is that it is not a problem, but the intended and expected behaviour.
Where did anybody explain that mails would remain in Thunderbird if you delete them via your phone in an IMAP account? Thunderbird or any mail client on your Mac/PC has nothing to do with that.

The default IMAP procedure is that everything remains on the mail server (at the mail provider) and you have access to everything via possibly different devices of your choice.
If you delete mails via your phone in your IMAP account, they are gone on the server, that’s why you would delete them (normally).

However …
In K-9 mail, you can go to Settings - Account settings - Fetching mail - When I delete a message (I hope, German locale here) … and set it so your deletions in K-9 don’t get mirrored on the server, that should help if I understand your intention correctly.

Edit: Found documentation …


I agree to AnotherElk.
Here my handling with the purpose of not having to much private data on my mail providers storage (to reduce damage of a hacked account or provider’s server a little bit):
I also use Thunderbird (TB) with IMAP. Every 6 to 12 months I copy mails, which are older than 1-2 years, to a local folder (in german TB: “Lokale Ordner”) naming the folder “Archive” with 1 folder for each year in it. After that I just delete the copied mails in my inbox, so they are deleted on the server, too. Of course, I backup the whole TB folder on my PC with all other personal files from time to time to a USB hard drive.

Thanks to both for your reply, I am not sure if i was not very clear then…
Actually when I delete messages FROM THE SERVER (in order to make space), it automatically deletes the same messages on Thunderbird as well. I had understood that the whole point of Thunderbird is to save all your messages on your computer, regardless of what’s going on in the server; this is written everywhere. IMAP is useful for being able to get messages on several devices at the same time. With IMAP the difference is that I would have to delete manually my messages on the server; but I thought normally it shouldn’t erase then on NY computer, no?
This is my whole point, I don’t know if I am clearer !
So actually the info I missed is that I have to save everything besides first?

With IMAP you don’t save all the messages to your computer. All the messages are on the server, they are not stored on your computer.


If you say “everywhere”, can you show us an example?

1 Like

@ Lidwien, sorry i don’t get your point… On Thunderbird you get all your messages to work offline don’t you?? And moreover there is an option to tick, “save all messages on your computer” which I did…

For me it seems, that you maybe mix up using Thunderbird on your PC with using a tool to backup your mails (for which Thunderbird can be used, too, of course).
So, much of the aspects you describe about your expectations of Thunderbird with IMAP fit better on the other very common protocoll named POP3, besides synchronization between the clients and the server (mail provider). Maybe looking for a Wikipedia entry for both protocols could help you understanding which features each of them have. With both there are possibilities to configure your client tool (K9-mail and/or Thunderbird) in addition to the standard features to come as close to your needs as possible.

I think the Thunderbird setting “keep messages for this account on this computer” implies “as long as the message is saved on the server”.
One thing you could try is set Thunderbird to save your archived messages in local folders.
To do that create a local folder named “archive”, then go to your account settings -> “copies & folders” and choose “keep message archives in”: other -> local folder -> archive.
Now just don’t delete messages anymore to free cloud space, but archive them instead.


No. Please read this …

Especially of importance is this point:

"Benefits of IMAP

The IMAP protocol supports both online and offline activity. Therefore, messages can be stored both on the local machine and on the server, enabling numerous benefits:

  • Multiple clients can be used to access messages. 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.

  • Thunderbird users can download their messages to their local system and access them even when they are not connected to the internet.

  • Messages load faster when they are stored on a local drive. Search performance is much faster than searching a set of messages on a remote server. Full-text search of a message body is only possible on messages that have been downloaded.

In order to provide this kind of flexibility and functionality, though, messages must be synchronized between the local machine and the email server."

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

You can configure Thunderbird to download the mails to your computer automatically (like you did), but that is only done for convenience, e.g. accessing them when offline or speeding up searches.
If you delete a mail in Thunderbird, it gets deleted at your IMAP account as soon as Thunderbird synchronizes the account. If you use whatever else to delete a mail at your IMAP account, it gets deleted in your Thunderbird as soon as Thunderbird synchronizes the account.
With an IMAP account, Thunderbird is only a tool to work with the mails on the server (with some convenient advanced features), as is the mail App on your phone.

If you want to keep your mails in Thunderbird before deleting them on the server, make yourselve some folders in the “Local Folders” in Thunderbird for organizing and then copy your mails there.

Alternatively you could use the POP protocol instead of IMAP, but that will probably end in a total mess of things if you use more than one device to access your account.


The posts here are maybe a bit long and technical. In summary this is the expected behaviour of Thunderbird, and if you don’t want it, then you should ask Thunderbird people how to fix this - maybe they know a way around. While many of us (including me) are Thunderbird users, we aren’t experts on Thunderbird settings.

The answer is you set up thunderbird to use pop, but ensure thunderbird is set up to never delete emails on server.

That’s not really the answer, since the available server storage for riseup accounts is very small.

What Kevin_Pugh says is what I do, too. I have Thunderbird with a pop account, it saves the whole E-mail on my PC without erasing it on the server.
Mails that are on my PC won’t be deleted from the PC although I delete them on the server via my Fairphone.

What should be wrong with that? To keep free space on the server, I can delete my mails via IMAP. To keep them, I can bring them to my PC via Pop. I think, Leti974 has a IMAP Account on Thunderbird, too.

There’s nothing wrong by doing that.
It’s your way of doing things. I like to use IMAP, just another choice.

Yes, but the problem Leti974 has is, that mails will be deleted in Thunderbird, if he deletes them on the server.

This cannot happen with a pop account.

1 Like

Bingo, mail clients using POP3 have support to keep message on server as well as deleting them. IMAP4 is supposed to be synced between clients. That’s one if its primary features in the first place.

What you (I’m not specifically talking to OP here) can do though is use OfflineIMAP. It basically copies your IMAP content over to Maildir which can be read locally by an e-mail client. I know it works with e.g. Mutt. Thunderbird I’m not sure. Its available in Homebrew (the defacto standard macOS package manager) and in various Linux distribution repositories. Its CLI, but not very complex.

1 Like

Thanks to all for your help and contributions…
@Paula, yes I will definitely try to archive them.
@ AnotherElk : yes this is exactly what I meant :
“Thunderbird users can download their messages to their local system and access them even when they are not connected to the internet.”

@moritzheintz : very interesting point! But when you check some of your mails on your phone (with POP3), then your laptop won’t download these mails anymore, right? Therefore you loose some of them… Or maybe you use another trick to prevent that?

… and to configure the mail App on your phone the same way (if it can be configured that way) … and hope nothing resets or changes those settings in your mail clients :wink: .

The phone can use IMAP. The device with Thunderbird can use pop and if I recall, you can sent Thunderbird to download all the message or just headers using pop.

Either way, IMAP is set up to use the nail database stored on the webmail site.

Pop can download the email to your local machine and with Thunderbird, delete the webmail server copy when you delte the email in Thunderbird.