For those thinking about migrating from #Proton to any other mail provider - that is how I did it👇
1. The export tool Proton offers (Proton Mail Export Tool) works. It lets you select your mailbox (one or multiple) and exports the files to a folder on your disk as EML, JSON including attachments. You do not loose anything.
2. Importing mails using Thunderbird works flawless. Connect your new account and either do:
2.1 Copy your exported mails from your disk into the "Local Folders" of Thunderbird and then use "Copy To" which syncs mails to the new providers mail server. The better option.
2.2 Just drag 'n drop the files from your disk into the inbox of your new account in Thunderbird. The good option.
2.3 There is also a Thunderbird Extension (ImportExportTools NG) that can import folders. I never used it. Just to mention it here.
For me the second one (2.2) worked without any issues. I got all mails, attachments, correct threats - no issues.
