Fastmail vs Proton Mail for Custom Domain Email: Which to Pick?

Fastmail vs Proton Mail for custom domain email is the choice most people land on once they decide to stop hosting their real address at a free provider. Both are paid, both are independent, both take a domain you own. They win on very different axes, and the axis that matters most on a custom domain is not features — it is what happens to your daily workflow after the DNS records are in.

This is a two-product decision framed entirely around custom domains. If you are comparing broader alternatives to Gmail, our three-way Fastmail, Proton Mail and iCloud post is a better starting point. Here we pick a genuine winner per dimension and are honest about which reader should choose which. Prices and plan limits change; verify the current numbers on each vendor's own page before you buy.

The verdict up front#

For a personal domain that you want to use like normal email — read on any device, in any client, with fast search and generous aliases — Fastmail is the better default. Setup is a guided flow rather than a documentation exercise, IMAP and JMAP work in every mail app you already use, and full-content search including attachments runs on the server so it is instant on a fresh device.

Choose Proton Mail if end-to-end encryption on your own domain is a genuine requirement, not a nice-to-have. Proton is the only side of this comparison that encrypts message contents so the provider itself cannot read them, and if that property is what you are paying for, nothing Fastmail does around it substitutes. You are trading away frictionless third-party client support and unrestricted server-side search to get it, and both of those trade-offs are real.

The honest concession: Proton Mail has built harder on the encryption side of custom domain email than Fastmail has, and if you need message contents that even the host cannot read, Proton is the answer and Fastmail is not. Everything else in this post is why we still recommend Fastmail for most people.

At-a-glance comparison#

The table below compares the dimensions that actually decide the purchase for a custom domain, rather than a feature list neither product loses on. Numeric limits and plan boundaries change — treat them as shape, and confirm the current values on the vendor's page at write time.

Where Fastmail wins#

Fastmail wins on the boring stuff, which on a custom domain turns out to be most of the stuff. The DNS setup is the first thing you notice. On a supported registrar it is close to a click; on the rest it is a wizard that fills every record for you and tells you which one has not propagated yet. There is nothing to learn about DKIM selectors or SPF alignment — you paste, you save, you wait a minute, and it verifies.

The bigger win is that Fastmail behaves like email should. Standard IMAP, SMTP and JMAP mean the mail account works in Apple Mail on your Mac, Outlook on your PC, Thunderbird on Linux, the default app on iOS and Android, and any AI-native email client you might layer on top. Nothing has to run a local proxy, nothing has to sit on the desktop to relay messages, and the same account works identically on a phone as on a laptop. That single property removes a whole class of decisions from your life.

Search is the third real advantage. Because Fastmail can read your mail, the server can index every word of every message and every attachment, and search returns instantly on a fresh install. You are not waiting for a local index to build. You are not choosing between searching metadata quickly and searching content slowly. On a domain you will use for years, that difference compounds — an inbox you can actually find things in stays useful; one you cannot quietly stops being an archive.

Aliases and calendars round out the practical case. Fastmail's alias and Masked Email support is generous and works with Bitwarden if you want throwaway addresses per site, and the Fastmail calendar and contacts sync into any CalDAV or CardDAV client rather than living inside a walled app. It is a plain email provider that does the plain email job unusually well.

Where Proton Mail wins#

Proton Mail wins the moment your requirement includes end-to-end encryption on message contents. That is not marketing; it is an architecture decision that changes what the provider can see. On Proton, message bodies are encrypted with keys the provider does not hold, so a subpoena, a rogue employee or a server breach does not hand over your mail. On Fastmail — as on Gmail, Outlook and effectively every non-encrypted provider — the host can read what is stored to run search and spam filtering, and that is an intentional trade for the convenience above.

For a personal domain that carries sensitive material — a journalist's tip line, a therapist's client mail, a founder's legal correspondence, or simply a strong personal preference for a host that cannot read your inbox — Proton is doing something Fastmail does not do at all, and no amount of Fastmail's polish substitutes.

Proton also wins on the ecosystem around encrypted mail. Aliases via SimpleLogin (now Proton-owned) are excellent, Proton Calendar and Contacts extend the same encryption to your schedule and address book, and Proton Unlimited bundles VPN, Drive and Pass under one price if you want the full privacy stack on one bill. If your reason for leaving Gmail is a coherent privacy posture rather than a single-feature complaint, Proton is the whole answer rather than one piece of it.

The Swiss jurisdiction matters to some readers and does not to others; treat it as a factor if your threat model involves specific legal regimes, and ignore it if it does not. Proton publishes their transparency reports and abuse policy; check the current version on proton.me/support before making it load-bearing.

The encryption trade-off in daily use#

The reason this comparison is not a wash comes down to what encryption does to workflow. Because Proton cannot read your mail, IMAP in a third-party client requires Proton Mail Bridge — a small desktop app that runs locally, decrypts messages, and exposes an IMAP/SMTP endpoint on 127.0.0.1 that Apple Mail or Thunderbird connects to. Bridge is included on paid Mail plans and only runs on macOS, Windows and Linux. There is no mobile Bridge, which means on iOS and Android you use the official Proton Mail app or nothing.

That constraint is fine if the Proton app is the app you want. It is a problem if you have a workflow built around Apple Mail on the Mac and the default Mail app on iPhone, or around a specialised client that only speaks IMAP. Fastmail imposes none of that: any client, any device, any day.

Search behaves the same way. Server-side search is impossible when the server cannot read the mail, so Proton search downloads the encrypted archive to your device and indexes it locally in what Proton calls Content Search. It works, and it is genuinely private, but the index has to build on every new device, and a phone or a browser session that has not fully indexed will only search subjects and senders. Fastmail's server-side search is instantly complete on any device you sign into.

Pricing model — check the current numbers on the vendor page#

We do not publish competitor prices in these posts because they change and the number in a blog post ages the day a plan is renamed. What you can rely on is the packaging shape — that changes less often and is what actually differs between the two.

Fastmail is per-user and single-product. You pick a tier that changes the storage, alias count, custom-domain cap and multi-user shape (individual, Duo, Family), pay monthly or annual, and that is the full offer. There is a free trial rather than a permanent free tier. The mental model is a paid email host and nothing else.

Proton Mail has a free tier with limits (typically one address on a Proton domain, not on a custom domain), then paid Mail plans that add the custom domain, more storage and Bridge. The Proton Unlimited plan bundles Mail with Proton VPN, Proton Drive and Proton Pass at a single price — worth it if you want the whole suite, less obviously worth it if you only want mail. Business plans are per-user with admin controls.

Two practical implications. First, if you already pay for a VPN or a password manager separately, Proton Unlimited can be cheaper than the sum of what you already spend. Second, if you only want mail, compare Fastmail against the Proton Mail-only plan and not against Unlimited — the like-for-like comparison is much closer, and the encryption is what you are actually paying the difference for.

Who each is genuinely for#

The clearest way to choose is by naming the reader each is right for and being honest about who should stop reading and go buy the other one.

Fastmail is right for you if you want a paid, independent email host that behaves like a normal mail account: works in every client, syncs into any calendar, indexes attachments on the server, and takes ten minutes to set up on a custom domain. Freelancers, consultants, solo founders, families sharing a domain, and anyone leaving Gmail for something that still looks and feels like email on every device. If you were going to describe your requirement as "just good email on my own domain", Fastmail is your answer.

Proton Mail is right for you if the reason you are leaving Gmail is that Google can read your mail, and the reason you want a custom domain is not to project professionalism but to own the identity your encrypted mail arrives at. Journalists, activists, therapists, lawyers with a specific practice profile, security researchers, and anyone whose threat model includes the host itself as an adversary. If your requirement is "my provider must not be able to read this", Proton is the only side of this comparison that meets it.

Where you should stop reading and go buy something else: if you need a shared team inbox with delegation and internal comments, neither of these is what you want — look at Front, Missive or Hiver. If you need Exchange calendar features against a corporate directory, look at Microsoft 365. If you want the cheapest possible custom-domain mail hosting and are willing to run a bit more infrastructure, Migadu or Zoho Mail are cheaper.

A third option, honestly#

A custom domain is a hosting choice, not a client choice, and this comparison is genuinely between two hosts. AI Emaily is not a hosting provider — we do not sell inboxes on our own domain, we sell an AI-native email client that connects to the inbox you already have. So we do not belong in the table above, and putting our row at the top of a provider comparison would be a category error a reader who understands the stack would catch in ten seconds.

Where we do fit is on top of Fastmail (and Gmail, Outlook, iCloud or any IMAP account). Once your custom domain is running on Fastmail, AI Emaily gives it a triage layer, drafts written in your voice via a user-set Context brain and per-client profiles, semantic search across the whole inbox, and Copilot or Autopilot autonomy modes with mandatory approval-before-send in Copilot, undo, and a full audit trail. If your reason for wanting a paid host is that you take email seriously, adding a client that helps you keep up with it is the natural second half. We build AI Emaily, and the honest limit is that we do not currently connect to Proton Mail — Bridge exposes IMAP locally to a single desktop client at a time, and we are a cloud client, so a Proton account is not on our supported list today.

That is the adjacent thing we actually do. If you pick Fastmail, our custom-domain guide shows the connection flow. If you pick Proton, the Proton Mail app and Bridge on desktop are the right pairing until we ship Proton support.