However, because of the auto Inbox filtering issue, I cannot recommend them as a provider for TB, unless security is extremely important to you. It seems like retrieving message through their Bridge software is a bit slow, but it's tolerable. Other than that, I have not had any major issues using it with TB, including any related to the creation of sub-folders or that sort of thing. I filed a bug report with Protonmail, then quite a while later, they closed the bug report because they could not reproduce the problem - so it's never been fixed. As a partial workaround I installed an TB addon named New Folder Filters Button that lets me run the filters by clicking on a Toolbar icon (after first selecting the Inbox folder). At some point last year, after an update to their bridge software, the automatic filtering I had set up for my Protonmail Inbox quit working, and mail messages would just accumulated in it until I run the filters associated with the account manually. I've been using a (paid) Protonmail account with Thunderbird for a couple of years now. I then created a filter to move the shopping emails from the ProtonMail Inbox to the Local Folders > Amazon, Insurance, etc. I was able to overcome this problem for my online shopping emails by creating a separate offline account in Thunderbird that I named Local Folders. Perhaps someone with a deeper understanding of how email programs function can provide some insight.

However all the mail that is in the Thunderbird Inbox is decrypted. I'm not sure I follow their logic but I can see where you might be defeating the purpose of having encrypted mail if you are going to scatter the incoming mail to the winds. Even though you can create sub folders and filters on the ProtonMail platform you are not allowed to do the same within your Thunderbird account for the ProtonMail for some reason. The only problem I have run into is ProtonMail puts all incoming mail into the Inbox on their server by default. I very recently became a paid ProtonMail user and I have found the interface between ProtonMail and Thunderbird works very well.

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