SMTP · paid plan + custom domain

How to connect
Proton Mail.

Use Proton’s hosted SMTP with a paid Mail plan, a custom-domain address, and a dedicated SMTP token.

Connection preview. You can read this guide and save a mailbox for later. Live authorization and warm-up remain off. Do not enter real credentials while the connection form is disabled.

Before you start

  • A paid Proton Mail plan and an active custom-domain address.
  • An SMTP token paired with that sending address.

Step-by-step setup

  1. Check SMTP eligibility

    Use a custom-domain address hosted by Proton. Standard @proton.me and @protonmail.com addresses are not eligible for this hosted SMTP path.

  2. Generate a dedicated SMTP token

    In Proton Mail, open Settings → All settings → IMAP/SMTP → SMTP tokens. Generate a token named MailboxWarm for your custom-domain address. Copy the displayed username and token; do not use your account password.

  3. Choose Other provider in MailboxWarm

    Open Mailboxes → Add mailbox, choose Other provider, and enter your sending email address. Named SMTP services all use this same Other provider connection option.

  4. Enter the connection details

    When connections are enabled, enter the SMTP values listed below. Choose Test & connect. MailboxWarm checks authentication and the encrypted connection without sending a message.

Connection settings

Match these values to the fields in MailboxWarm. Keep passwords and keys private.

Connection option
Other provider
SMTP host
smtp.protonmail.ch
Encryption / port
STARTTLS / 587
SMTP username
The custom-domain address paired with the token
SMTP password
Your generated Proton SMTP token

SMTP sends; it does not read your inbox. This connection does not include IMAP access to your mailbox. Placement and rescue activity concern the controlled seed inboxes receiving warm-up messages. Provider-specific compatibility still needs live validation.

Check the result

In today’s preview, expect Mailbox saved for later. When connections are enabled, a successful check shows Mailbox connected, with warming still paused. A failed connection check is not proof of delivery or a reason to add the same mailbox again.

Once live warming is available, choose the mailbox’s plan and schedule before starting. Connecting alone does not begin warm-up, and your provider’s sending limits still apply.

Open setup preview

Troubleshooting

SMTP tokens is unavailable

Check your paid plan and custom-domain address. This is not a connection for free Proton accounts.

Can I use Proton Mail Bridge?

No. Bridge connects desktop mail clients through software on your computer. MailboxWarm requires a publicly reachable SMTP service and cannot connect to your local Bridge.

The token fails

Check the paired address and generate a replacement if the token was revoked. SMTP submission is not end-to-end encrypted.

Provider resources

Provider menus and account policies can change. Use their official documentation for the latest requirements.

Settings reviewed September 12, 2026 · Documentation review, not a live connection test.