The following is a list of the codes for the stages and their meanings.
| Phase | Description |
|---|---|
| 0 | while not connected |
| 1 | while idle |
| 2 | during MAIL FROM |
| 3 | after MAIL FROM |
| 4 | during RCPT TO |
| 5 | after RCPT TO |
| 6 | during DATA |
| 7 | after DATA |
| 8 | while sending BODY |
| 9 | reading confirmation |
| 10 | during EHLO |
| 11 | after EHLO |
| 12 | reading BANNER |
| 13 | during RSET |
| 14 | after RSET |
| 15 | during STARTTLS |
| 16 | after STARTTLS |
| 17 | handshaking TLS |
| 18 | renegotiating TLS |
| 19 | during XCLIENT |
| 20 | after XCLIENT |
| 21 | out of band bounce |
| 22 | in unknown state |
Code 21 is the only message disposition notification (MDN). With the exception of 22, which is unknown, all other stages occur during the SMTP transaction. In other words, they are in-band bounces.
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