If you have questions about SMTP, the Internet mail message-header
format, or the Internet mail infrastructure, try my reference manuals:
http://cr.yp.to/smtp.html
http://cr.yp.to/immhf.html
http://cr.yp.to/im.html
You don't have to suffer through the RFCs; I did all the work for you.
Russ Allbery writes:
> RFC 821 says that x5y status codes are for mail system problems, while x0y
> status codes should be used for syntax errors:
In this case, RFC 821 is obsolete. A subsequent RFC added code 555 for
certain syntax errors.
> draft-ietf-drums-smtpupd-10.txt seems to agree.
smtpupd-10 is garbage. See http://cr.yp.to/smtp/klensin.html for further
explanation. In this case, Klensin simply screwed up.
---Dan
