sendmail, 4th Edition

$i

---

The queue identifier

All versions

Each queued message is identified by a unique identifier (Section 11.2.1). The $i macro contains as its value that identifier. Prior to V8.6 sendmail , $i had a value assigned to it only when a file was first placed into the queue. Beginning with V8.6 sendmail , $i is also given a value when the queue file is processed .

$i is not used by sendmail internally, nor should you use it in a rule set. It should be trusted for use only in the Received : and Message-ID : headers.