What is an autoresponder?

Autoreplies arrive with headers built to be recognized. Auto-Submitted: auto-replied and X-Autoreply exist so that software can filter them, and a well-built system does.

The information they leak is often useful. Out-of-office notices routinely name a colleague, a direct phone number and a return date, which is more than most enrichment tools provide.

One category is worth acting on: the notice saying the person has left the company. That is an explicit signal to remove the address before it is recycled into something worse.

Verification cannot see any of this, because an autoresponder fires on delivery and a verification connection closes long before a message exists.

Say you send 5,000 outreach emails on a Monday and 210 automatic replies come back by Tuesday. Treat them as a data import. A quick sort finds 170 ordinary out-of-office notices, 28 saying the person no longer works there, and 12 giving a new email address.

The 170 tell you when to follow up. If the notice says back on the 14th, a reply on the 9th is wasted, and a sequence step can be pushed past the return date. The 12 are updates to apply, carefully, since the person gave that address to correspondents and not to your marketing list. Those last 28 are removals, and often they name a successor worth a fresh, personal introduction.

Here's the kind of text you're parsing: I'm out of the office until June 14 with limited email access. For urgent matters contact Sam Ortiz at 555-0142. One short note has given you a date, a colleague and a phone number.

RFC 3834 sets the conventions. A well-behaved autoresponder adds Auto-Submitted: auto-replied to what it sends. Check for that header first, then for older habits such as X-Autoreply, X-Autorespond and Precedence: auto_reply. Many automatic replies also arrive with an empty envelope sender, which shows up as Return-Path: <>.

The same standard says responders should stay quiet for mail that looks like a mailing list. If your message carries List-Id or List-Unsubscribe headers, or Precedence: bulk, a compliant responder won't answer it. That's why a newsletter triggers far fewer out-of-office replies than a plain one-to-one email to the same people.

It also says the reply should go to the envelope sender and not the From address. On a sending platform, that means some autoreplies land in your bounce-processing mailbox instead of your inbox, where they're usually discarded. If you want them, ask your platform whether it can forward non-bounce mail received at the return path.

Microsoft adds a header you can send: X-Auto-Response-Suppress: OOF, AutoReply asks Exchange not to generate them.