# ADR 002: Route custom-domain inbound mail to free Proton

- HTML version: https://robbiepalmer.me/projects/personal-digital-infrastructure/adrs/002-cloudflare-routed-proton-mail
- Project: Personal Digital Infrastructure (https://robbiepalmer.me/projects/personal-digital-infrastructure.md)
- Status: Proposed
- Date: 2026-10-18
- Initiatives: Digital Twins for Everyday Life (https://robbiepalmer.me/initiatives/digital-twins-for-everyday-life.md)

# Context

The custom domain already uses Cloudflare. Proton Mail is attractive, but Mail
Plus costs $47.88 per year and the immediate requirement is a durable inbound
address rather than a full mailbox migration.

[Cloudflare Email Routing](https://developers.cloudflare.com/email-routing/)
can map custom-domain addresses and catch-all patterns to a verified Proton
destination. It forwards incoming mail. It does not make free Proton send as
the custom domain, and it does not provide an ordinary mailbox or sent folder.

Proton requires a paid Mail plan to host a
[custom domain](https://proton.me/support/custom-domain) for normal sending and
receiving. Cloudflare's separate Email Service can send through SMTP or an API,
but operating that path would add client integration, delivery monitoring, and
sent-mail retention.

# Decision

Start with Cloudflare Email Routing forwarding the custom domain to the free
Proton mailbox. Continue sending from the Proton address. Do not buy Mail Plus
solely to receive custom-domain mail.

The trial must verify:

* each intended address reaches Proton and rejects unintended destinations;
* SPF, DKIM, DMARC, and Cloudflare routing records are documented;
* forwarded messages retain enough original headers for filtering and later
  Inbox Signal ingestion;
* replies visibly use the Proton address, so no one mistakes forwarding for
  custom-domain sending;
* the domain can be repointed to another mailbox without changing public
  contact addresses; and
* export and recovery work from a clean Proton session.

Revisit paid mailbox hosting when sending or replying as the custom domain is a
regular need, Proton Bridge is required, or the Proton bundle has already been
justified by Pass and VPN. At current prices, Mail Plus is
[$47.88 per year](https://proton.me/pricing). Unlimited is $119.88 per year and
includes three custom email domains with paid Pass, VPN, and 500 GB of shared
storage.

# Alternatives

## Use Proton Pass custom-domain aliases

Pass Plus supports custom domains for aliases and can
[initiate mail from an alias](https://proton.me/pass/pricing). If the Pass trial
in [ADR 001](/projects/personal-digital-infrastructure/adrs/001-proton-pass-trial)
succeeds, test this before buying Mail Plus. It may cover custom-domain replies
and new messages, but it remains an alias forwarding system rather than a full
mailbox with ordinary IMAP or Bridge behaviour.

## Buy Proton Mail Plus now

This gives the cleanest custom-domain sending and receiving experience. It also
adds Bridge access, more addresses, filters, and Proton-managed domain signing.
Defer it until outbound identity or those mailbox features matter in practice.

## Operate outbound mail through Cloudflare Email Service

This keeps the provider split and supplies SMTP and API sending. It also turns
a simple personal mailbox into an operated mail system. Reconsider it for
automated messages, not as the first answer to ordinary personal replies.

## Move directly to Proton Unlimited

Unlimited makes sense if the Pass and VPN trials succeed because its renewal
price is almost identical to those products bought separately. Buying it for
inbound mail alone would spend $119.88 to solve a free forwarding problem.

# Consequences

The custom domain becomes a portable inbound identity at no new subscription
cost. Outbound messages expose the Proton address, and some correspondents may
reply to it directly. The project accepts that limitation until real usage
justifies paid hosting.

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