> Ned Freed <ned.freed@xxxxxxxxxxx> wrote: > > > > > What's wrong with 5.1.2 and 5.1.8 ? > > > > > X.1.2 Bad destination system address > > > > > The destination system specified in the address does not exist > > > or is incapable of accepting mail. For Internet mail names, > > > this means the address portion to the right of the "@" is > > > invalid for mail. This code is only useful for permanent > > > failures. > > > > > X.1.8 Bad sender's system address > > > > > The sender's system specified in the address does not exist or > > > is incapable of accepting return mail. For domain names, this > > > means the address portion to the right of the "@" is invalid > > > for mail. > > > > Wrong group of codes. Those are status for mail systems to return, not > > the routing layer. > The point of null MX records it to explicitly say the address is invalid, > so an address status would seem to make sense. No, the point is to say that a host is invalid. > X.1.XXX Addressing Status > The address status reports on the originator or destination > address. It may include address syntax or validity. These > errors can generally be corrected by the sender and retried. > An invalid address isn't a problem with the DNS itself. Neither is a NXDOMAIN error, and that's in the 4.z group. > X.4.XXX Network and Routing Status > The networking or routing codes report status about the > delivery system itself. These system components include any > necessary infrastructure such as directory and routing > services. Network issues are assumed to be under the control > of the destination or intermediate system administrator. > Looking through the X.4.X codes, I can't tell whet is the distinction > between 5.1.2 and 5.4.4. The text for X.4.4 has a weird description of a > nodata / nxdomain response, which is exactly the same as "does not exist" > under X.1.2. Again, it's a question of what component is involved. 4.x codes are for directory services external to the mail system, 1.x is for the mail system itself. Which admittedly leaves LDAP in a bit of an odd position. Oh well. > A DNS lookup returning only an SOA (Start of Administration) > record for a domain name is one example of the unable to route > error. > There's evidently a lot of overlap and lack of precision in how these > codes are defined and used so I don't think it matters in practice what > this draft picks. On the contrary, it matters because the DNS changes constantly, and the code may be all you have telling you what the condition was that caused the bounce. Ned