19 rules in 4 groups, worth 100 points in all. They were set before any product was scored and apply the same way to all 9.
Version 1, published 9 Oct 2026
In short
Each rule is a yes-or-no fact, a list (such as the systems with an app) or a number with published thresholds, read from the vendor's own pages.
A fact the vendor does not publish earns nothing. A feature in beta or preview does not count.
The list follows the points. A tie goes to the lower price on "cost for a team of 5", then to the name.
Paid or free mailbox hosting on your own domain, for teams of 1 to 50, used in a web browser on Windows or any mail app. All numbers refer to a team of 5 mailboxes on the cheapest paid plan with a custom domain and at least 5 GB per mailbox (a pooled allowance is divided by 5). Encrypted-mail services, desktop mail apps and forwarding-only services are left out.
Price 22 points
Rule
What it takes
Points
Cost for a team of 5
The cheapest paid plan with a custom domain and at least 5 GB per mailbox (a pooled allowance divided by 5), for 5 mailboxes, in US dollars a month, billed yearly, at the regular price without introductory discounts. A flat price per domain counts in full. If a vendor page shows another currency, use its US price page; a euro-only vendor is recorded in EUR. $5 or less earns 12 points, $10 or less 9, $20 or less 6, $40 or less 3, $60 or less 1.
12
Free plan on your own domain
A free plan (not a trial) that hosts at least one mailbox on a domain you own. A free plan that only gives addresses on the vendor's domain does not count.
6
Monthly billing
The cheapest paid plan with a custom domain can be bought month to month, with no yearly commitment, at a published monthly price.
4
Mailbox 29 points
Rule
What it takes
Points
Storage per mailbox
Mail storage per mailbox on the cheapest paid plan with a custom domain, as the vendor states it. Storage pooled with files counts at the stated amount per user; storage pooled across a whole account or domain is divided by 5. 50 GB or more earns 10 points, 25 GB or more 7, 10 GB or more 5, 5 GB or more 2.
10
Open mail and calendar protocols
The vendor's help pages state support for each protocol on the cheapest paid plan with a custom domain, so any standard mail app can connect. Each one earns 2 points.
8
Shared calendar and contacts
Every mailbox on the cheapest paid plan with a custom domain comes with a calendar and an address book, and users can share calendars with each other.
5
More than one domain
The cheapest paid plan with a custom domain can host two or more of your own domains under one subscription, as the vendor states on a pricing or help page.
3
Aliases and catch-all
On the cheapest paid plan with a custom domain, a mailbox can have extra addresses (aliases) and the domain can have a catch-all address, both documented in the vendor's help.
3
Security 28 points
Rule
What it takes
Points
Two-factor sign-in
Two-factor or two-step sign-in with an authenticator app or security key is available to every mailbox on the cheapest paid plan with a custom domain, not only by SMS.
7
Passkeys or security keys
Sign-in with a hardware security key or passkey (FIDO2 or WebAuthn) is documented as generally available for mailboxes on the cheapest paid plan with a custom domain.
3
Admins can require 2FA
An administrator can require two-factor sign-in for all users of the domain on the cheapest paid plan with a custom domain.
3
Single sign-on (SAML)
Users can sign in through SAML single sign-on with your identity provider, on at least one plan for teams of up to 50.
5
SOC 2 Type II or ISO 27001
The vendor names a SOC 2 Type II report or an ISO/IEC 27001 certification for this product or the company running it.
6
SPF, DKIM and DMARC guides
The vendor's own help pages explain how to set up all three of SPF, DKIM and DMARC for a custom domain on its service.
4
Reliability and support 21 points
Rule
What it takes
Points
Written uptime commitment
A written uptime commitment of at least 99.9% for the mail service, in terms or an SLA page, that gives service credits or a refund when missed, on the cheapest paid plan with a custom domain.
9
Public status page
A public status page for the mail service that shows past incidents.
2
Live support
Live chat or phone support is included on the cheapest paid plan with a custom domain, as the vendor states on a pricing or support page. Ticket-only support, help articles and community forums do not count.
4
Mail migration tool
The vendor offers a documented tool or free service that moves existing mailboxes from another provider by IMAP or a similar method, on the cheapest paid plan.
3
Official phone apps
The vendor publishes an official app for both iOS and Android for these mailboxes.