Email auto-responder

Your second stack: pull a package that replies to email. Deploy it, mint a mail host, send it a message, get an auto-reply back — all on the hosted service.

Where hello, world answered the web, this one answers email. You’ll pull the auto-responder package — two rules that accept inbound mail and reply once, with the loop protection a real auto-responder needs — then give it a mail address with a single command. No inbox to host, no DNS to configure.

Note

Cloud or local? This tutorial uses the hosted service (free tier), where inbound mail “just works.” To run it locally instead, txco dev --personalities=cron,web,admin,lmtp boots a chassis with the mail head and you drive it with swaks over LMTP — see the inbound-mailbox example and lmtp.md. The cloud path below is the simplest.

If you’re continuing from the last tutorial you’re already signed in. Otherwise:

txco login

2. Pull the package

mkdir autoresponder && cd autoresponder
txco install auto-responder --as autoreply

  ✔ verified: signed by txco [SHA256:…]
installed auto-responder 0.1.0 as stack "autoreply/_mail" (2 files)

Review OPS/autoreply/, then run `txco apply` to deploy.

auto-responder is a mail package — its rules live in a _mail channel, not the web scope. --as autoreply nests that channel under your chosen stack name, so it lands at OPS/autoreply/_mail/. (--as renames the base and keeps the channel; for the web hello-world package the same flag just renamed the stack.)

Read what you’re about to run:

cat OPS/autoreply/_mail/0/accept.txcl OPS/autoreply/_mail/100/reply.txcl

# 0/accept.txcl — accept every inbound recipient (250) so mail lands.
WHEN @src == "lmtp"
  EMIT @lmtp.res.code = 250, @lmtp.res.msg = "accepted"

# 100/reply.txcl — reply once, skipping bounces and other auto-replies.
WHEN @lmtp.is_bounce == false && @lmtp.msg.headers.auto-submitted == ""
  SET ._sendmail.to            = @lmtp.mail.from,
      ._sendmail.from          = @lmtp.rcpt.0,
      ._sendmail.subject       = &concat("Re: ", @lmtp.msg.subject),
      ._sendmail.body          = "<p>Thanks for your message! This is an automated reply.</p>",
      ._sendmail.envelope_from = "<>",
      ._sendmail.campaign      = &concat("autoreply:", @lmtp.msg.id)
  EXEC "txco://sendmail"

The reply goes from the address that was written to (@lmtp.rcpt.0) to the original sender (@lmtp.mail.from). Three guards stop mail storms: skip bounces (@lmtp.is_bounce), skip anything already Auto-Submitted, and an at-most-once campaign keyed on the inbound Message-ID. The null <> reverse-path is the RFC-3834 auto-reply convention.

3. Deploy

txco apply

autoreply/_mail v1 activated (2 files)

No URL is printed — a mail stack has no web channel, so it doesn’t auto-mint a host. You mint one in the next step.

4. Give it a mail address

txco auth tenant hostnames add --mint --stack autoreply

minted autoreply-a1b2c3.stacks.thanks.computer → prod-you/autoreply
  routes immediately (verified + DKIM); mail to <anything>@autoreply-a1b2c3.stacks.thanks.computer reaches autoreply/_mail

That host is both your inbox (mail to it routes to autoreply/_mail) and a verified, DKIM-signing sender (so the reply passes the recipient’s anti-spoof checks) — minted on demand, no DNS to set up.

5. Email it

From your real inbox, send a message to any address at that host:

To: hello@autoreply-a1b2c3.stacks.thanks.computer
Subject: testing

Within a few seconds you get a reply: “Thanks for your message! This is an automated reply.” — from hello@autoreply-a1b2c3.stacks.thanks.computer, DKIM-signed.

Change it

Edit the body (or swap the canned reply for an ai://chat draft so the answer is written by a model), then ship again:

# edit OPS/autoreply/_mail/100/reply.txcl …
txco apply

What you just did

You deployed an email auto-responder to the hosted service: pulled a mail package, applied it, minted a verified mail host, and replied to real email — with loop protection built in. From here:

sendmail / lmtp — the full outbound + inbound mail contracts.
Packages — bundle and publish your own.
AI — make the reply a model draft instead of a canned message.