The following is cut and pasted from RFC821:
For each command there are three possible outcomes: "success"
(S), "failure" (F), and "error" (E). In the state diagrams below
we use the symbol B for "begin", and the symbol W for "wait for
First, the diagram that represents most of the SMTP commands:
----------->| E |
+---+ cmd +---+ 2 +---+
| B |---------->| W |---------->| S |
+---+ +---+ +---+
| 4,5 +---+
----------->| F |
This diagram models the commands:
HELO, MAIL, RCPT, RSET, SEND, SOML, SAML, VRFY, EXPN, HELP,
NOOP, QUIT, TURN.
I hope that error is really processed like failure but I still don't know...
Anyone out there know?
On 14 Jun 1995, Michael Harer wrote:
dee @ cybercash.com ("Donald E. Eastlake") writes:
This is really an RFC 821 question, but can anyone tell me what
typical SMTP clients do if they get a 3xx reply after a MAIL or RCPT
RFC 821 says this is an "error" as opposed to a "failure" but do they
(1) abort the whole conversation, (2) give up on that piece of mail,
or (3) (for RCPT) just treat it like a failure and go on to the next
recipient, or (4) something else I haven't though of?
I'd appreaciate any info on this.
The following excerpt from rfc1123 briefly mentions "interoperability
have arisen" but I didn't see anything that describes a required "action" for
this occurrence. I also didn't see where (in rfc821) a 3xx reply was
categorized as an "error" as opposed to a "failure" but only general
that receivers must adhere to the listed reply codes. This is an interesting
question that I am also looking for additional clarification.
5.2.10 SMTP Replies: RFC-821 Section 4.2
A receiver-SMTP SHOULD send only the reply codes listed in
section 4.2.2 of RFC-821 or in this document. A receiver-SMTP
SHOULD use the text shown in examples in RFC-821 whenever
A sender-SMTP MUST determine its actions only by the reply
code, not by the text (except for 251 and 551 replies); any
text, including no text at all, must be acceptable. The space
(blank) following the reply code is considered part of the
text. Whenever possible, a sender-SMTP SHOULD test only the
first digit of the reply code, as specified in Appendix E of
Interoperability problems have arisen with SMTP systems
using reply codes that are not listed explicitly in RFC-
821 Section 4.3 but are legal according to the theory of
reply codes explained in Appendix E.
Donald E. Eastlake 3rd +1 508-287-4877(tel) dee(_at_)cybercash(_dot_)com
318 Acton Street +1 508-371-7148(fax)
Carlisle, MA 01741 USA +1 703-620-4200(main office, Reston, VA)