The best paid Calendar alternative to Proton Mail is Posteo. If that doesn't suit you, our users have ranked more than 50 alternatives to Proton Mail and five of them are paid Calendar Apps so hopefully you can find a suitable replacement. Other interesting paid Calendar App alternatives to Proton Mail are mailbox, Fastmail, Kolab Now and Mailture.
Web- and IMAP-based email service. 2GB cost 1€/month. Information is hosted on encrypted hard drives. Electricity from renewable resources is used.
Almost everyone thinks Posteo is a great Proton Mail alternative.
Posteo is the most popular commercial alternative to Proton Mail.
E-mail inbox, online office, cloud storage, and video conferencing. Business or personal plans. From 1 € /month (1.10 USD).
Mailbox.org is a partial replacement for Protonmail. It offers a fully functional email solution (email, calendar, contacts), but with the added benefits of PGP encryption support (you can handle the keys or let them do it). It also allows you to send links to people who don't use PGP if you want to send private messages. For the encryption, it's a bit like Protonmail. For everything else, it's like a privacy-respecing Gmail alternative.
Almost everyone thinks mailbox is a great Proton Mail alternative.
Fastmail offers secure email hosting with comprehensive webmail services, including IMAP, POP, and SMTP protocols. It supports file sharing, shared folders, large mailboxes, instant messaging, and is compatible with popular email programs. Excellent for businesses with compliance features.
Kolab Now provides a suite of intuitive apps in a user friendly environment to make your day to day online comms easier, smarter and most importantly; secure.
Mailture, a secure, business-oriented email service, is made to cater to all your emailing needs. With top-notch collaboration and communication features, Mailture offers much more than your usual inbox.
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Posteo could be a good Protonmail alternative. It offers email encryption in a similar way: Posteo's people, government surveillance and successful hackers won't get into your email content. It also offers a calendar feature, which protonmail users have been crying out for for years.