RelayMailPricing

Forward email to Slack / Fastmail

Forward a Fastmail address (support@) to a Slack channel

On Fastmail, support@ is usually an alias on your domain. Point the alias at your RelayMail address, or add a rule that sends a copy there, and each email starts a Slack thread. Replies from the thread go back to the customer as email.

Steps

  1. 1

    Option A: deliver the alias to RelayMail

    Go to Settings > My email addresses and open support@ (or Add address > Create an alias). Under Delivery options choose "Deliver to another address" and enter the forwarding address from your RelayMail setup page (inbox-...@relay.relaymail.app). Save. New aliases can take up to 15 minutes to work.

  2. 2

    Option B: a rule that sends a copy

    Go to Settings > Filters & Rules > Create rule, add a To/Cc/Bcc condition for support@yourdomain.com, then choose the "Send a copy to" action with your RelayMail address and Save. A rule runs Fastmail's spam filter first.

  3. 3

    If forwarded mail doesn't arrive

    An admin can turn on SRS: Settings > Users & Sharing > Team settings > SRS. It applies to every user in the account, so Fastmail suggests it only when forwarded mail isn't arriving.

  4. 4

    Send a test email

    Email support@ from an outside account. When it arrives, RelayMail confirms forwarding by itself and the email appears in the channel as a thread; reply there and the sender gets your reply by email.

Confirming the forward

Fastmail's forwarding, alias and rules pages describe no confirmation email for a new destination: you enter it and save. If one does arrive, RelayMail passes it on to the email on your Slack account until forwarding is confirmed. Replies you write in the Slack thread go out from noreply@relay.relaymail.app with Reply-To set to your support address, so the customer's answer comes back through the same forward into the same thread. To send replies as support@ itself, verify your domain in RelayMail (see the custom domain guide); that adds sending records for RelayMail and does not change where your inbound mail goes.

What to watch for

  • Alias forwarding skips Fastmail's spam filter; a rule runs it first. Rules don't forward messages that were filtered as spam.
  • Forwarding breaks SPF for the original sender. Fastmail keeps the original envelope sender by default; SRS rewrites it to srs.messagingengine.com.
  • Custom domains need at least one account admin on a plan above Basic, and the domain must have Fastmail handle mail delivery.
  • Use a normal alias for support@; Masked Email addresses are random.

Questions

Alias or rule for forwarding Fastmail to Slack?

An alias delivery target forwards everything sent to support@ without spam filtering. A "Send a copy to" rule filters spam first and keeps a copy in Fastmail.

Why does forwarded Fastmail mail not arrive?

Fastmail points to SPF: forwarding breaks it for the original sender, and turning on SRS in Team settings is its suggested fix.

Answer Fastmail email from the Slack thread

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Updated 2026-11-07. How we check these pages. Sources: Fastmail: Set up mail forwarding, Fastmail: How to set up aliases, Fastmail: Filters & Rules, Fastmail: Account limits, Fastmail: Custom domains.

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