Comparison · Verified July 2026 · Every claim links to its source
ASTIS Mail vs Proton Mail for Business
Proton is a superb email provider. ASTIS Mail is not a provider at all — it encrypts on top of the one you already have. That single difference decides most evaluations.
TL;DR. Proton Mail is the most successful private-email company in the world — 100M+ accounts, Swiss foundation ownership, SOC 2 Type II and ISO 27001. It is also a replacement provider: business adoption means repointing your domain’s MX records to Proton. Two documented details decide many evaluations: Proton does not end-to-end encrypt subject lines (a PGP-interoperability limit they state themselves), and search over encrypted mail needs a fragile per-device local index — the top complaint in its business reviews. ASTIS Mail encrypts subjects, filenames, and calendars client-side and rides your existing Gmail/Microsoft 365. If migration is on the table, Proton is excellent. If it isn’t, that is what ASTIS Mail is for.
At a glance
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| ASTIS Mail | Proton Mail for Business | |
|---|---|---|
| What it is | E2EE client over your existing Gmail / M365 | |
| Migration required | None — OAuth connect, mail stays in your mailbox | |
| Subject lines encrypted | ||
| Search over encrypted mail | Mailbox search via your provider as usual | |
| Desktop clients / IMAP | Native apps (macOS · Windows · Linux) + Thunderbird add-on — no Bridge needed | |
| External recipient (no account) | One-time key invite (browser client) | |
| Calendar | E2EE calendar over your provider | |
| Certifications issued today | ||
| Jurisdiction | ||
| Published pricing | ||
| Scale & track record | New product, no public review base |
Where is the trust boundary?
Every product on this market draws a line: everything left of it cannot read your content; everything right of it you have to trust. The only question that matters is where the line sits.
Keys generated and used client-side. No service can produce plaintext.
Content encrypted, but a vendor-run key server authorizes every decryption.
Encryption and access control live in the vendor’s server-side platform.
TLS in transit; content readable at rest by providers and gateways.
For Proton-to-Proton message content the boundary is the device — genuine E2EE. But subjects stay outside E2EE, and inbound external mail arrives in plaintext before zero-access storage. The bigger boundary is organizational: Proton must become your provider first.
Where your data lives
ASTIS Mail deliberately does not host message content: decrypted mail exists only on your devices, ciphertext rides your own mailbox. Compare where each product puts plaintext.
Who holds the keys?
ASTIS Mail’s model
Same PGP heritage, opposite deployment: OpenPGP + WKD on top of the provider you already run. Body, subject, attachments, and filenames sealed on-device; capsule metadata is keyed by address hashes, and no content ever touches ASTIS.
The founder-level premise: if everyone has to migrate to one inbox, the solution will not work for most companies. Gmail keeps doing delivery and uptime — it just can’t read the payload anymore.
Proton’s model
PGP-based E2EE, automatic between Proton users; open-source, audited apps. Mail from the outside world arrives over TLS in plaintext and is then encrypted at rest with your public key (“zero-access”) — meaningful protection, but the message transited readable and its subject stays outside E2EE.
Adoption is a provider change: domain verification, deleting your existing MX records, Easy Switch migration, Bridge for desktop clients, a parallel ecosystem for docs and storage.
“Subject lines in Proton Mail messages are not end-to-end encrypted… to ensure interoperability.”— proton.me/support — encryption explained
Shared standard, different boundary
Both products speak OpenPGP — keys are portable and messages are decryptable by any compliant implementation. The difference is where the product boundary sits: Proton draws it around a new provider you migrate into; ASTIS draws it inside the provider you already have. Same cryptographic family, opposite adoption cost.
What stays readable
What is actually inside each product’s E2EE envelope.
Proton: subjects protected only by zero-access storage, not E2EE (their docs); inbound external mail arrives via TLS then is encrypted at rest; E2EE calendar sharing is Proton-to-Proton only. ASTIS: E2EE applies to ASTIS-enveloped correspondence; unencrypted inbound Gmail mail stays as-is.
The migration question — the honest section
When migration is where projects die
A 60-person firm on Google Workspace — shared drives, delegated mailboxes, admin policies, integrations — rarely survives “everyone migrates.” The real comparison becomes Workspace + Proton vs Workspace + ASTIS Mail, because most firms keep Workspace anyway.
ASTIS Mail connects via OAuth in an afternoon. Encrypted mail travels through Gmail or Microsoft 365 as ciphertext; nothing repoints, nobody retrains on a new provider.
When switching providers is right
A new company with no legacy, or a team ready to adopt the whole privacy suite — Mail, Drive, Docs, VPN, Pass — gets real value: $6.99–12.99/user/mo, mature audited apps, a decade of reputation.
Proton’s Easy Switch tooling is genuinely good: automatic Gmail import with ongoing sync during a gradual cutover.
Pricing
ASTIS Mail
- Solo $179/year · Team $15/seat/mo · Organization $20/seat/mo
- Self-serve, 30-day trial, no services engagement
- 25-seat firm: ≈ $4,500–6,000/year
Two honest shortlists
Pick Proton Mail for Business if
- Businesses ready to change email providers — especially new companies with no legacy
- Teams that want one privacy suite: mail, VPN, storage, passwords, docs
- Issued certifications today: SOC 2 Type II, ISO 27001
- A decade of reputation and open-source, audited clients
Pick ASTIS Mail if
- Organizations staying on Google Workspace / Microsoft 365 — by choice or IT reality
- Confidentiality bar includes subject lines and metadata, not just bodies
- EU-entity vendor with no US hyperscalers in the stack, as a procurement line item
- E2EE calendar over the provider you already run
FAQ
Does Proton Mail encrypt subject lines?
Not end-to-end. Proton documents this: subjects remain outside PGP encryption for interoperability, protected only by zero-access storage. ASTIS Mail encrypts subjects client-side.
Can I use Proton for Business without migrating my domain?
Proton on your company domain means repointing MX records — Proton becomes your provider; their setup guide instructs deleting existing MX records. ASTIS Mail attaches to your existing provider via OAuth; nothing repoints.
Which is more private for mail I receive from outsiders?
Different mechanisms: Proton encrypts all inbound mail at rest with your key (zero-access) after TLS transit. ASTIS Mail leaves your inbound Gmail mail where it is; its E2EE covers ASTIS-enveloped correspondence. For your outbound confidential mail, ASTIS’s envelope is wider — subject included.
Is ASTIS Mail audited like Proton?
Proton has SOC 2 Type II and ISO 27001; ASTIS’s SOC 2 Type II is in progress (July 2026). ASTIS publishes signed builds, open specs, and an inspectable SDK in the meantime — verify, don’t trust.
Sources — retrieved July 2026
- Proton: encryption explained (subjects not E2EE)
- Proton: custom domain setup (MX repoint)
- Proton: password-protected emails
- Proton Bridge (IMAP, paid plans)
- Proton: search encrypted content
- Proton SOC 2 announcement
- Proton business pricing
- ASTIS security whitepaper
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Don’t trust either vendor — verify.
Read the security documentation, then run the 30-day trial on your existing Gmail or Microsoft 365 mailbox. Keep the provider. Protect the content.