I don’t know if this helps, but here are my two pennies: Like mentioned by others before, I think you actually want to be using POP3, instead of IMAP. I use Thunderbird on my computer and K9 on my fairphone. I use POP3 in my private (not so much storage) account as follows:
I have it set up that mails are deleted from the server as soon as I either
a) delete them in K9 (that would be a K9 setting) or
b) check emails on my computer,. i.e. download them into thunderbird (where they then either stay and are archived into folders or are deleted from my computer as well).
For my work account (loads of storage space) I use a mix of IMAP and POP3. I use IMAP in K9 (set to sync the last 20 emails) and and POP3 in Thunderbird (set to not delete emails after downloading - i.e. they are downloaded POP3 style onto my computer, but also remain on the server - and even if I delete them on the server, the Thunderbird content is not affected).
No, wrong, as each POP3 device/client keeps it´s own local synchronization protocol. As long as mails are not deleted on the server each POP3 client will download them and update it´s own synchronization protocol individually.
Therefore a POP3 configuration in Thunderbird would require to tick the option “delete the mail from the server when it is deleted in the local folder”. And also untick the option “keep mails on the server” (so further devices/clients may also download them).
With these options set it should show a similar behavior as an IMAP configuration relating to synchronizing and deleting.
I’d be careful with features like that. I’ve burned my hands more than once with features like that in POP3, causing missing mails or double mails. Especially with heavy volume and unstable connections (dial-up comes to mind). POP3 isn’t suitable for this task. Swap to a mail provider who provide IMAP4. Anything less is <= 90s standards.
If I already checked a mail on my Phone, my PC with Pop configuration afterwards loads them down but shows them as already seen. That’s exactly what I want.
My Pop-account configuration I put to “save a copy on the server” and “delete the copy after 30 days”.
If I delete mails on my IMAP-Account before loading them down via pop3, they are deleted anyway and I won’t see them on my PC. That works very well with SPAM-Mails, which I can delete on the smartphone very fast and easy without loading them down.