# What is mail on TurboStack?

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](configure.md).

## 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](deliverability.md) 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.

> [!WARNING]
> A mail-catcher is a development tool only. When it is on, outbound mail is captured, not delivered.
> Never leave it enabled on a production host, or real mail (password resets, order confirmations)
> silently disappears.

## 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.

## Related

- [Configure mail on TurboStack](configure.md)
- [Mail deliverability](deliverability.md) - authenticate your domain and fix mail landing in spam.
- [SMTP error codes](smtp-error-codes.md) - what a `5.7.x` rejection means and how to fix it.
- [Email](../../platform/hosts/advanced/email.md) - Mail Settings on the host's Advanced tab.
- [Connecting your domain](../../getting-started/connecting-your-domain.md) - where to add DNS records.