Okay, I got my domains back at #FastMail, and was excited to see they import from #Proton, so theoretically I could get those couple weeks of email back into my FastMail account. But it asks for an MBOX file and Proton exports stuff into .json and .eml.
Any idea how to get Proton emails over to FastMail? Or what an MBOX file is?
MBOX is a pretty universal email database file. Fastmail lists it as an option on their import tool. On the Import tab of the Migration page in Settings you'll see it partway down.
@hollie @jessekelber It'd surprise me if Proton doesn't provide an IMAP option. (Basically acting as an email client and downloading your mails.)