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CloseDeveloper reply by dmrhn
Rated 3 out of 5 stars
Not bad BUT if we receive any mail, we are not notified.
Protonmail ask to allow desktop notification but of course we can't.
As mentioned in the description, it is a simple button that opens the site in Thunderbird, the rest is all about Thunderbird's built-in browser.
To create your own collections, you must have a Mozilla Add-ons account.