In article <1116377042.592906.137650@g44g2000cwa.googlegroups.com> you write:
Hello all. We have a client containing an underscore in the email address domain name. Our email server rejects it because of it's violation of the RFC standard. This individuals claim is that he doesn't have problems anywhere else and if this is going to be a problem he's "going to take his business elsewhere"!
I understand it's a violation of the standard, but does it pose a security hole to the email server to allow this sort of mail?
Thanks
RFC 952 and RFC 1123 describe what is currently legal in hostnames. Underscore is NOT a legal character in a hostname. Before anyone says that domain names allow underscore which they do. RFC 1034 Section 3.3 For hosts, the mapping depends on the existing syntax for host names which is a subset of the usual text representation for domain names, together with RR formats for describing host addresses, etc. Because we need a reliable inverse mapping from address to host name, a special mapping for addresses into the IN-ADDR.ARPA domain is also defined. Mail domains follow the same rules as for hostnames. RFC 821 and its replacement RFC 2821 havn't extended the syntax to include underscores. Mark