Fastmail vs Proton Mail for a Business Inbox: Search, Encryption, Export and Price

Fastmail and Proton Mail are the two names that come up whenever a small business wants to leave Google Workspace or Microsoft 365 without landing on a hobby provider. Both are good. They are optimised for different anxieties, and most of the regret people describe after switching comes from choosing on the wrong one. This is a comparison of what each one is actually built to do, from the two companies’ own documentation and pricing pages, so that the choice can be made on the anxiety that applies to your inbox rather than the one that sounds more responsible.

The one design decision everything else follows from

Proton Mail uses zero-access storage for message bodies and attachments; that protection does not cover every email field or every delivery route. Its own description of the search feature makes the consequence explicit: to search the body of your messages, the app builds an index in your browser, and “you must create an index of your messages for each browser on each device that you access Proton Mail with.” The index never leaves the device, it does not survive clearing browser data, it does not work in private browsing, and for a very large mailbox Proton warns that the index may need more storage than the browser offers, in which case a date limit appears showing how far back content search reaches. Proton’s help pages describe body search for the web app; its mobile search documentation covers subject, sender and recipient and states that advanced syntax cannot search message content.

Fastmail documents server-side processing of readable data for search and calendar notifications. It encrypts stored mail and connections to its service, but this does not exclude the provider from accessing message contents. For delivery to another provider, transport encryption depends on the other server supporting it.

What encryption covers in a business conversation

Situation	Proton Mail’s documented protection
Stored message body and attachments	Zero-access encryption, including received external mail
Subject and sender/recipient addresses	Encrypted, but not end-to-end encrypted
Mail between Proton addresses	End-to-end encrypted automatically
Ordinary delivery to an external address	TLS transport; the recipient’s provider may access the message
External contact needs end-to-end protection	Use password-protected mail or a compatible PGP workflow; a password-protected message can receive an encrypted reply

Encryption scope checked October 12, 2026 against Proton’s encryption explanation and Fastmail’s security documentation. This is a documentation comparison, not a security audit.

For a hypothetical client exchange, map both mailboxes and the sending method before promising confidentiality. A provider choice alone does not establish the protection of the whole conversation. Keep sensitive details out of subject lines and agree on a workable recipient process before sending real client material.

Plans and prices side by side

Prices below are for one user. Keep currencies and billing periods separate: an advertised monthly equivalent on an annual plan is not a month-to-month bill. Fastmail’s US page excludes tax; Proton’s business page says taxes may apply. Confirm the final currency, tax and renewal amount before paying.

Plan	Monthly billing	Annual billing: total (monthly equivalent)	Storage per user	Custom domains / decision point
Fastmail Business Basic	US$4	US$36 (US$3)	5 GB mail/calendar/contacts + 1 GB files	Mixed-plan domain exception below; no third-party mail clients
Fastmail Individual / Business Standard	US$6	US$60 (US$5)	50 GB mail/calendar/contacts + 10 GB files	Custom domains and third-party clients
Fastmail Business Professional	US$10	US$108 (US$9)	100 GB mail/calendar/contacts + 50 GB files	Adds retention archive
Proton Mail Plus	€4.99	€47.88 (€3.99)	15 GB shared with Drive	1 domain; single user
Proton Unlimited	€12.99	€119.88 (€9.99)	500 GB shared with Drive	3 domains; single user with bundled services
Proton Mail Essentials (business)	Not verified in this check	US$83.88 (US$6.99)	15 GB	3 domains; 10 addresses per user
Proton Workspace Standard (business)	Not verified in this check	US$155.88 (US$12.99)	1 TB	15 domains; broader team bundle

Prices and listed allowances checked October 12, 2026 against Fastmail US pricing, Proton personal plans and Proton business pricing. The retrieved Proton business page showed annual totals; monthly-billing prices were not independently confirmed. No checkout purchase was performed.

Personal plans are a solo-inbox comparison, not a substitute for pricing a centrally managed team. For a hypothetical three-user team on annual billing, Fastmail Standard totals US$180/year and Proton Mail Essentials US$251.64/year, before tax or extras. Those are calculations from the listed seat prices, not quotes. Compare the client-access and storage requirements below before treating the US$71.64 difference as a saving. The documentation does not establish why either company chose its price.

Fastmail separates mail/calendar/contact storage from file storage. Proton’s personal plans list storage shared with Drive, so document storage can affect the remaining mailbox allowance. Compare the capacity your team actually needs, rather than treating each total as dedicated mail space.

Custom domains and setup

Both handle a custom domain the same way: you add DNS records, both provide a wizard that checks them, and both then support DKIM and SPF for the domain. Proton Mail Plus supports one custom domain and Unlimited three; Fastmail Basic does not include a standalone custom domain, but its business accounts have a mixed-plan exception: one Standard or Professional administrator can share a domain with Basic users. Domain access and third-party mail client access are separate entitlements. If you run several brands from one inbox, Proton’s per-plan domain limits are the number to check first, because it is the one most likely to push you up a tier.

Can your team keep its existing mail apps?

Requirement	Fastmail	Proton Mail
Use a third-party desktop mail client	Eligible plans use an app password; Basic excludes IMAP and SMTP	A paid Mail plan and Proton Mail Bridge provide desktop IMAP/SMTP access
Keep Basic users on a company domain	A multi-user Business account needs at least one Standard or Professional administrator to share the domain	Not a Proton plan rule; compare its own user and domain allowances
Use Bridge on a phone	Not applicable	Bridge supports macOS, Windows and Linux, not mobile devices

Client access and Fastmail domain exception checked October 11, 2026 against Fastmail plan selection, Fastmail app passwords and Proton IMAP/SMTP setup. These are documented capabilities, not compatibility tests. The price table has its own October 12 check date.

For a hypothetical three-person team, price each seat against its actual needs. A Fastmail Basic user who shares the company domain still cannot use a third-party mail client. If everyone needs one, a mixed-plan domain arrangement does not remove that requirement. With Proton, identify which computers can run Bridge and test the chosen client before moving the domain. Proton also documents full-text search through Bridge, so the browser-index limitations above do not describe every desktop workflow.

Before changing mail routing, use non-sensitive sample messages to check sending, receiving, attachment search and export in the exact apps your team intends to use. Record the app, operating system and plan alongside the result. This is a suggested acceptance check, not a test performed for this article.

The bundle question

Proton Unlimited and the Workspace business plans include a VPN, the Proton Pass password manager and Drive storage. For a solo operator that consolidation has real value: one bill, one account, one company to trust or not. Whether it is worth paying for depends on whether you would otherwise buy those pieces separately. A password manager on a free tier covers most individuals, and a VPN is only worth counting if you would actually run one, so the honest comparison is Proton’s bundle price against the sum of what you would genuinely pay elsewhere, not against the list price of three products. Fastmail sells email, calendar, contacts and files and nothing else, which is either a limitation or a relief depending on how you feel about tools that replace several others.

Getting your mail out again

An export file and a usable replacement inbox are different deliverables. Check the scope before moving the company domain:

Export route	Documented output and limits	Decision before leaving
Fastmail web export	ZIP download from Settings → Migration → Export; one folder at a time, capped at 4 GB per export. Subfolders need individual exports.	Inventory folders and date ranges so a successful download does not hide missing mail.
Fastmail through a desktop client	An alternative on plans with third-party access; Basic excludes it. Fastmail recommends offline copies of all folders and large attachments.	Confirm the client downloaded more than the Inbox before treating its archive as complete.
Proton Mail Export Tool	Available to all users on Windows, macOS and Linux; exports decrypted messages as EML and metadata as JSON. Its restore function accepts backups made by this tool.	Keep the EML and JSON files together for that restore route; check the destination client’s import support separately.

Export scope checked October 11, 2026 against Fastmail’s download guide and Proton’s Export Tool guide. These are documented capabilities, not migration tests.

Proton names Thunderbird and Outlook as destinations for EML messages. That does not establish that either imports Proton’s accompanying JSON metadata or recreates every label and folder. Its tool also excludes Calendar, Drive and Pass data. A business using the bundle needs separate export plans for those products. Paid users can also use the Bridge route described above.

Before cancelling, import a small, non-sensitive sample into the intended destination and compare message dates, attachments, folders and labels. Record any differences instead of assuming a readable message proves a complete migration. Protect local decrypted copies appropriately; the export is outside the provider’s mailbox protection. This is a proposed reader check, not a test performed for this comparison. It is worth knowing what an export contains before choosing a destination.

Keeping the same custom-domain address can avoid changing that address in every outside account, although mail routing and authentication still need a migration plan. If the address itself changes, inventory the services that use it for sign-in, recovery or invoices. That dependency work belongs in the cost of migrating tools, separate from downloading the mailbox.

Where the data lives

Fastmail is an Australian company that stores customer data on servers in the United States, and since August 2026 offers an EU data residency option on its own servers in Amsterdam; European customers were moved there by default and everyone else can choose at signup. Fastmail states that it complies with valid law enforcement requests and notifies account holders where possible. Proton is Swiss; the stored-content protection described above should not be read as a claim that all account information and email metadata are inaccessible. Provider access is one criterion; this comparison does not establish suitability for any regulated profession. Define the confidentiality, retention and access requirements of the actual workflow before choosing. The same logic applies when choosing a messaging app that encrypts by default.

A way to decide

Say you run a three-person consultancy and the inbox is the business record: contracts, invoices, four years of client threads that get searched from a phone in a meeting. Server-side search across the whole archive, with no index to rebuild on a new laptop, is the feature that gets used every day, and the provider’s ability to read the mail is a risk you can assess and accept. That case is Fastmail.

If limiting provider access to stored message contents is a requirement, evaluate Proton alongside the recipient workflow in the encryption table. Then check search in the actual apps your team will use: browser indexing and desktop Bridge are different workflows, as the client-access section explains.

Make the decision against three acceptance criteria: who must be unable to read the contents, which recipient workflow is practical, and which search and export tasks the team needs. Use non-sensitive samples to verify the workflow before committing the business domain.

Additional documentation: Search and encryption behaviour from Proton: search message content, Proton: how to search, Fastmail: how Fastmail provides a secure service and Fastmail: choosing your data residency. Export details from Proton Mail Export Tool and Fastmail: download all your data. Prices change; the live pages win.