Send automatic replies only to mail from people

How to do it

Two systems that answer each other's automatic mail loop until a quota runs out. Out-of-office replies, ticket acknowledgements and bounce notices are the usual pair. RFC 3834 sets the rules. Skip mail marked as automatic, skip mailing lists, and send the reply to the Return-Path address, never to From or Reply-To. Keep a record of who got an automatic reply and when, and suppress repeats for 7 days, the period RFC 3834 suggests. Mark the messages you send on your own as Mark automated messages says.

Examples

JavaScript example

const REPLY_GAP_MS = 7 * 24 * 60 * 60 * 1000;

export function mayAutoReply(headers, lastRepliedAt, now = Date.now()) {
  const auto = (headers['auto-submitted'] ?? 'no').toLowerCase();
  const precedence = (headers.precedence ?? '').toLowerCase();
  if (auto !== 'no' || headers['list-id'] || ['bulk', 'list', 'junk'].includes(precedence)) return false;
  return !lastRepliedAt || now - lastRepliedAt > REPLY_GAP_MS;
}

Python example

from datetime import datetime, timedelta, UTC

REPLY_GAP = timedelta(days=7)

def may_auto_reply(headers: dict, last_replied_at: datetime | None) -> bool:
    auto = headers.get("auto-submitted", "no").lower()
    precedence = headers.get("precedence", "").lower()
    if auto != "no" or "list-id" in headers or precedence in {"bulk", "list", "junk"}:
        return False
    return last_replied_at is None or datetime.now(UTC) - last_replied_at > REPLY_GAP

How to check

Feed the inbound handler a message with Auto-Submitted: auto-replied, one with a List-Id, and two normal messages from one sender within a day. Only the first normal message gets a reply, and that reply carries Auto-Submitted: auto-replied.

Sources

• RFC 3834, Recommendations for Automatic Responses to Electronic Mail

Related rules

• EML-7 Mark automated messages in Email