KoltrixFastmail vs Proton Mail for Small Business Email
Fastmail and Proton Mail are the two independent mailbox hosts small teams ask about most. How they differ on privacy, desktop clients and daily team use.
On this page(10 sections)
- The short version
- Fastmail: a standards-first mailbox host
- Proton Mail: an encryption-first mailbox host
- Side by side
- How each feels for a small team
- Shared addresses
- Onboarding non-technical colleagues
- Working with customers outside the service
- When Fastmail is the better fit
- When Proton Mail is the better fit
- What neither one covers
- A quick decision checklist
- Bottom line
When a small team decides it doesn't want its company email inside Google or Microsoft, the shortlist usually comes down to two names: Fastmail and Proton Mail. They are both independent, both paid, both free of ads, and they make very different bets about what "better email" means.
This is a comparison of those bets, written for a team of two to twenty people choosing where their mailboxes should live. Everything below reflects each product at the time of writing; both companies ship often, so check their own pages before you commit.
The short version
Fastmail is built around speed and open standards. It wants to be the best possible conventional email service: fast web app, excellent search, full support for the protocols every mail client already speaks.
Proton Mail is built around encryption. It wants your mail to be unreadable to anyone but you, including Proton itself, and it accepts some convenience trade-offs to get there.
If you hold onto that one distinction, most of the detailed differences make sense.
Fastmail: a standards-first mailbox host
Fastmail has been running since 1999 and is based in Australia. Its reputation rests on a few things that matter day to day:
- Protocol support. IMAP, SMTP, CalDAV and CardDAV all work, so Apple Mail, Thunderbird, Outlook and phone mail apps connect without extra software. Fastmail is also one of the main drivers behind JMAP, a newer IETF standard for mail sync that its own apps use.
- Speed and search. The web interface is quick, and search across a large archive is one of the things long-time users praise most.
- Custom domains and aliases. Adding your own domain is routine, and aliases are easy to create, which suits small companies that want
hello@,billing@andsupport@without paying for extra mailboxes. - Masked Email. Fastmail can generate unique addresses per website, with a 1Password integration, so a leaked address can be switched off without changing your main one.
What Fastmail doesn't do is end-to-end encryption of your mailbox by default. Mail is encrypted in transit and at rest on its servers, like most mainstream providers, but Fastmail can technically access it. For most businesses that's the normal trade-off; for some it's a dealbreaker.
Proton Mail: an encryption-first mailbox host
Proton was founded in 2014 by a group that met at CERN and is based in Switzerland. Its core promise is end-to-end and zero-access encryption:
- Messages between Proton users are end-to-end encrypted automatically. You can also send password-protected messages to people on other providers.
- Stored mail is encrypted with keys Proton doesn't hold, so the company can't read your inbox even if asked to.
- Swiss jurisdiction is part of the pitch. Some teams care about that a great deal; others don't think about it.
- A wider suite. Proton also offers calendar, drive, password manager and VPN products, so a privacy-minded team can consolidate several tools under one account.
The trade-offs follow from the encryption. Because the server can't read your mail, traditional IMAP access isn't possible directly. Proton's answer is Proton Mail Bridge, a desktop app that decrypts locally and presents an IMAP/SMTP interface to clients like Outlook or Apple Mail. It works, but it's one more thing to install and keep running on every machine. Server-side search over message bodies is also more constrained than on a provider that can index plaintext.
Side by side
| Question | Fastmail | Proton Mail |
|---|---|---|
| Core strength | Speed, standards, search | End-to-end and zero-access encryption |
| Desktop mail clients | Native IMAP/SMTP | Via Proton Mail Bridge |
| Calendar and contacts | Yes, with CalDAV/CardDAV | Yes, within Proton's apps |
| Custom domains | Yes | Yes, on paid plans |
| Aliases and masked addresses | Yes, including Masked Email | Yes, plus hide-my-email aliases |
| Company base | Australia | Switzerland |
| Wider suite | Mail, calendar, contacts, files | Mail, calendar, drive, pass, VPN |
| Sending API for your app | No | No |
Prices and plan names change, so we're deliberately leaving them out. Both publish their business pricing on their own sites, and both price per user.
How each feels for a small team
Shared addresses
Small companies live on shared addresses. Both services handle aliases well, which is enough if one person owns support@. Once two or three people need to work the same address, neither is a shared inbox in the help-desk sense: there's no built-in assignment or "who's replying to this" view. Teams usually either share credentials (don't), forward to several people (messy), or add a separate shared-inbox tool.
Onboarding non-technical colleagues
Fastmail tends to be easier to hand to someone who just wants their mail in the client they already use. Proton is just as simple if everyone uses Proton's own web and mobile apps, and harder if people insist on Outlook or Apple Mail, because Bridge has to be installed and kept running.
Working with customers outside the service
Proton's end-to-end encryption is automatic only when both sides use Proton (or compatible PGP). Mail to customers on Gmail or Outlook is protected by normal transport encryption unless you use password-protected messages. That's worth understanding before you assume every customer email is end-to-end encrypted.
When Fastmail is the better fit
- Your team already uses a mix of desktop and phone mail clients and doesn't want to change.
- Search speed over years of archive matters to you.
- You want calendar and contacts that sync with standard protocols everywhere.
- Encryption at rest on a trusted provider is enough for your threat model.
When Proton Mail is the better fit
- Confidentiality is a core requirement: legal-adjacent work, journalism, sensitive client material, or simply a firm preference that your provider can't read your mail.
- Swiss jurisdiction is a real factor in your decision.
- You want encrypted mail, files and passwords from a single vendor.
- Your team is happy to live in Proton's own apps.
What neither one covers
Both are mailbox hosts. If your company also runs a product that sends password resets, receipts and notifications, you'll need a separate transactional email service, with its own DNS records and its own dashboard. Neither is designed for high-volume application sending.
That split is the reason some SaaS teams look at tools that combine the two. Koltrix, for example, is a team inbox plus a transactional API and SMTP relay on the same domain. The honest caveat: it has no IMAP access in its first release, so if desktop clients are a hard requirement, Fastmail fits better today. The comparison of Koltrix and Zoho Mail walks through the same mailbox-host trade-off with a different vendor, and our scorecard for choosing a provider gives you a way to weigh it for your own team.
A quick decision checklist
- Do we need end-to-end encryption, or is encryption at rest enough?
- Which mail clients does each person actually use today?
- Do several people need to work the same address, and how will we handle that?
- Does our app send email, and where will that live?
- Does company location or jurisdiction matter to our customers?
- Have we tested a trial with a real domain and real mail flow?
Bottom line
Fastmail and Proton Mail are both serious, well-run alternatives to the big suites, and neither is a wrong choice for a small business. Choose Fastmail if you want the fastest, most standards-friendly conventional mailbox. Choose Proton if encryption your provider can't undo is the point. And whichever you pick, plan separately for shared-address workflows and for the email your product sends, because neither mailbox host is built to solve those.
Start with Koltrix
Your domain, one inbox, and an API that sends.
A team inbox where AI sorts and drafts (nothing is sent without your click), plus the transactional API and SMTP relay your product sends with. 7 days free, no card.
