dalz

I pay like 5€/year with https://purelymail.com

I use it to synchronize media to my raspberry pi, which then runs restic daily to do the actual backup.

However, you shouldn’t use syncthing if you want to delete the files on your phone after they’re backed up, because they’ll disappear from the server as well. I think you can wrestle syncthing into handling this correctly, but it’s not advised as it’s not meant for backups.

For that I’ve been thinking about setting up immich or the like, but for now I have plenty of space on the phone ;)

You could use mbsync to automate this. You can configure it so that it downloads new mail with IMAP, but keeps them even if they are deleted from the server.

Then you will have a Maildir that you can manage with any mail client, index with notmutch, etc.