I will never made Proton Mail my default mail client until I can use it offline.

This app is completely useless without internet access.

It is illogical to create a desktop client that cannot work offline. I'm better off signing in to my web based account which has full functionality.

I installed this and immediately uninstalled it.

Do better.

Proton mail an calendar mac desktop apps gives have no real added value compared to accessing webmail and webcalendar.
It is indispensable that the emails and events be available even when the computer is offline

Seems like this is still not implemented yet (as of September 2025). At least it is missing in the current Mac Desktop version. If my Mac is offline Protonmail will reject to start up. This is annoying. I was thinking about switching my mail completely to Proton including my domains, but if offline functionality is not available, I won't do it.

Other email clients have this ability.
Important when travelling

Yes, working offline is a must. Especially in areas with sketchy Wifi such as airports and/or while on a flight.

100% agree with this. Offline access is a must-have, especially for people who travel a lot or work in areas with spotty internet. Even something as simple as replying to a service email or checking past communication with an appliance repair company becomes a hassle without offline support. Would love to see Proton handle this the way Gmail or Thunderbird does, queue everything and sync when back online.

Being able to work on your emails when offline is a must.

https://www.theverge.com/2023/12/14/24000696/proton-mail-desktop-app-mac-windows-encrypted
" Users will be able to look at a limited number of both read and unread emails while offline. "

Statement is vague since there is no user controllable mechanism to determine what/which Email and folders, incl. attachments to download and duration to keep for offline access for paid subscribers (unlike Thunderbird for example).

https://proton.me/blog/proton-mail-desktop-app

I lost internet access yesterday and when I launched ProtonMail there was nothing there... I should at least be able to read all the email that were available when I was last connected to the internet.

Agreed. Email/calendar that requires internet access just to load any content at all really lacks sufficient usefulness for the average person.

Please provide a Mac OS Desktop App for Off Line use and allowing login to multiple accounts. This would be helpful for Family plan.