1 Best Open-Source Alternatives to Proton Mail in 2026
By Noahlast updated
All 5 Proton Mail alternatives
Compared: open-source alternatives to Proton Mail
| Alternative | Best for | Standout | Biggest weakness | Learning curve | Price |
|---|---|---|---|---|---|
| Proton Mailreference | privacy-conscious individuals, journalists, and small teams who want end-to-end encrypted email with open-source, independently audited clients rather than a mainstream provider that can technically read stored mail | Zero-access encryption paired with open-source, independently audited client apps, so Proton itself cannot decrypt a Mail Plus or Unlimited inbox even under legal compulsion. | The free tier caps storage at just 1 GB and one address, and the higher-value Unlimited and Family tiers bundle VPN, Drive, and Pass features that email-only switchers may not need, pushing the effective per-mailbox cost above single-purpose providers like Fastmail. | Low | Free tier · paid from $3.99/mo |
| Tuta | privacy-conscious individuals and organizations, including journalists, healthcare providers, and nonprofits, who want end-to-end encrypted email and calendar with open-source, auditable clients | Post-quantum end-to-end encryption (TutaCrypt) covering both email and calendar by default, with fully open-source client apps auditable on GitHub. | No PGP or S-MIME support for encrypted mail to external, non-Tuta recipients, and no IMAP/SMTP access, so mailboxes only work through Tuta's own apps and webmail. | Low | Free tier · paid from $3.25/mo |
Proton Mail
Tuta1.Tuta — best Proton Mail alternative for privacy-conscious individuals and organizations, including journalists, healthcare providers, and nonprofits, who want end-to-end encrypted email and calendar with open-source, auditable clients
Tuta is the best Proton Mail alternative for users who want encryption that extends to the calendar as well as email, since Tuta encrypts both using TutaCrypt, a post-quantum cryptography scheme designed to resist decryption by future quantum computers, a scope Proton Mail's own end-to-end encryption does not extend to calendar entries in the same way. Both providers ship fully open-source, independently audited client apps and offer a free tier capped at 1GB of storage, matching each other at the entry level. Tuta's paid Revolutionary plan costs roughly $3.25/month (about €3, discounted on annual billing), below Proton Mail's Mail Plus at $3.99/month, though Tuta's Revolutionary tier includes only 20GB of storage versus Proton Mail's 15GB Mail Plus at a similar price point. Tuta has no external ratings on record in our listing data to compare against Proton Mail's 4.5/5 score from 122 Capterra reviews. Proton Mail is still the better choice for anyone who needs to connect a third-party email client or send encrypted mail to non-Proton recipients: Tuta does not support IMAP or SMTP at all, so its mailboxes only work through Tuta's own apps, and Tuta has no PGP or S-MIME support for encrypting messages to external recipients, while Proton Mail's Bridge app connects Mail Plus and Unlimited accounts to standard IMAP clients like Outlook.
Compared to Proton Mail: post-quantum TutaCrypt encryption covering both email and calendar, cheaper Revolutionary tier at $3.25/month, but no IMAP/SMTP or PGP support for external clients
Wins:Post-quantum TutaCrypt encryption applies to both email and calendar, a scope Proton Mail's encryption doesn't extend to calendar entries the same way · Revolutionary tier costs about $3.25/month, below Proton Mail's $3.99/month Mail Plus · Fully open-source clients (GPL-3.0) with F-Droid and direct APK distribution outside the Play Store
Loses:No IMAP or SMTP support at all, so mailboxes only work through Tuta's own apps, unlike Proton Mail's Bridge app for standard clients · No PGP or S-MIME support for encrypted messages to non-Tuta recipients, a gap Proton Mail's broader interoperability doesn't have to the same degree · No external ratings on record in our listing data, versus Proton Mail's 4.5/5 score from 122 Capterra reviews
Pros
- Post-quantum end-to-end encryption (TutaCrypt) applied to both email and calendar, not just message bodies.
- Fully open-source clients (GPL-3.0) available for independent security audit, plus F-Droid and direct APK downloads outside the Play Store.
- Revolutionary and Legend plans include unlimited calendars and labels, with custom domain support starting at the Revolutionary tier.
- Ad-free, with no tracking or behavioral advertising built into the business model.
Cons
- No PGP or S-MIME support for encrypted messages to non-Tuta recipients.
- No IMAP or SMTP access, so Tuta inboxes can only be used through Tuta's own apps and webmail, not third-party clients like Outlook or Thunderbird.
- Free tier is capped at 1GB storage with no custom domain or extra email aliases.
Pricing: Free tier · paid from $3.25/mo — Free (1GB) matches Proton Mail's free tier; Revolutionary ~$3.25/month (20GB) vs Proton Mail's Mail Plus at $3.99/month (15GB)