Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!usc!snorkelwacker!spdcc!rayssd!gmp From: gmp@rayssd.ray.com (Gregory M. Paris) Newsgroups: comp.mail.sendmail Subject: Re: sendmail and MB records Summary: Now that you mention it... Keywords: BIND, MB, MR, MG, MINFO, RFC1035 Message-ID: <139@rayssd.ray.com> Date: 17 Mar 90 02:40:31 GMT References: <1990Mar15.190444.14424@sobeco.com> Reply-To: gmp@quahog.ssd.ray.com (Greg Paris) Organization: Raytheon Submarine Signal Division Lines: 58 In an article stacy@sobeco.com (Stacy L. Millions) writes: > This may be a silly question (sendmail is just starting > to make sense to me), but is there a way to configure > sendmail to look up users via the MB records in the > nameserver? If you check the relevant RFC (1035 at this time), you'll see that MB, MR, MG, and MINFO are all "experimental" RR types. That said, coincidentally, I just happen to be experimenting with them. I modified 5.61 sendmail to look up MB and MR records. Coding-wise it's not really too tough. The real difficulty is in determining what's the "right" thing to do and in trying to anticipate problems (mail or alias loops, perhaps). For instance, the RFC says that the main use of MR records might be to provide forwarding for people who have left a domain. To me that implies that there might not be a corresponding MB record (it's in another domain, after all), yet if you check the 4.3 BSD BIND guide, it says there must be one. I coded it up so that the MB is optional, which seems preferable to me. Another question is how to interpret the NEWNAME value contained in an MR record. For instance, what if the NEWNAME is something like greg.paris.ssd.ray.com? Which dot do you convert to an @-sign? Perhaps this is the reason that the BIND document says an MB is required -- MB returning MADNAME, a hostname only, reducing the possibilities for confusion. (No, it doesn't eliminate them.) Another tricky thing is when to look up MR and MB records. Do you only look for them in the case of "user@domain," or do you also look for them when you have just "user"? The former might not buy enough to make implementation worthwhile, whereas the latter would raise the ire of users who wish to receive mail on more than one host. A possibility I was considering was to use multiple MB records. Say gmp wishes all mail to be stored on host "quahog" except for mail sent to "hilarious," which he wants stored there. The relevant MB records might look like this: gmp IN MB quahog gmp.hilarious IN MB hilarious The lookup procedure would be to query for MAILB info on user.thishost and honor that, if found. If not found, check for just user and honor that if found. Otherwise, use the traditional local delivery methods (check aliases, then check passwd, or no such user). I'm not sure if all this really buys that much, though. Is anybody interested in this, or is the reason why MB/MR/MG/MINFO are still experimental that it's not worth the bother??? Greg -- Greg Paris {decuac,necntc,uiucdcs,uunet}!rayssd!gmp Please call me Eddie if it will help you relax.