What is mail on TurboStack?

How outbound transactional mail works on TurboStack - the local mail service, DKIM domain authentication, the development mail-catcher, and when to use an external SMTP provider.

TurboStack is primarily an application-hosting platform, so mail is a supporting service rather than the main product. This page explains how outbound mail works on your host, so you can decide how to send mail and what to authenticate. For the steps to set it up, see Configure mail on TurboStack.

Outbound transactional mail

Your applications send outbound mail - password resets, order confirmations, notifications - through the local mail service on the host. This is delivery from the server to the outside world; it is meant for transactional mail, the low-volume messages your application generates as people use it.

You do not need external Simple Mail Transfer Protocol (SMTP) credentials for basic delivery. The application hands the message to the local mail service, which delivers it. TurboStack does not run mailboxes for receiving and reading mail - it is not an inbox or webmail host.

Domain authentication with DKIM

Receiving mail servers are strict about who is allowed to send mail for a domain. If they cannot confirm a message is genuine, they file it as spam or reject it. You confirm that your mail is genuine by authenticating your domain with three Domain Name System (DNS) records:

  • Sender Policy Framework (SPF) lists the servers allowed to send mail for your domain.
  • DomainKeys Identified Mail (DKIM) adds a cryptographic signature receivers can verify.
  • Domain-based Message Authentication, Reporting and Conformance (DMARC) tells receivers what to do when SPF or DKIM fail.

TurboStack generates the DKIM signing key for you. You set the sending domain and a selector under the host's Advanced > Mail Settings, then publish the record TurboStack produces. Publishing these records is the single most important thing you can do to land in inboxes rather than spam folders. See Mail deliverability for the full background.

The development mail-catcher

While you build and test an application, you often want to see the mail it sends without actually delivering it to real people. TurboStack offers a development mail-catcher that captures outbound mail so you can inspect it in a web interface instead of sending it.

When to use an external SMTP provider

The local mail service is fine for low-volume transactional mail. It is not the right tool for high-volume or marketing/newsletter sending. Bulk mail from a shared server IP almost always harms your sending reputation and gets the IP blocklisted.

For anything beyond low-volume transactional mail, send through a dedicated email/SMTP provider. You point your application's mail settings at the provider and publish the provider's SPF, DKIM and DMARC records. A provider also gives you delivery analytics, bounce handling and reputation management by default.

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