Re: Nameserver calls - libesmtp problem?

[Brian Stafford <brian stafford uklinux net>]

On Fri, 29 June 16:25 Albrecht Dreß wrote:

| Following a hint by Carlos, I now have these two lines in /etc/hosts:
| 
| 127.0.0.1       localhost       localhost.localdomain
| ::1             localhost       localhost.localdomain

Actually I didn't realise /etc/hosts did IP6 <sigh>

| Now, for local recipients (like root@localhost) your test program does *not*
| trigger the dial in any more, with both --host=:25 and --host=localhost:25. So
| if the resolver call is done as you explained, the config now seems to be
| correct, as it apparently first looks into the local files. It connects
| correctly with sendmail, and the mail is delivered correctly, too.

Phew, relief!!!!

| However, for *remote* recipients, now sendmail makes the querey between the
| messages
| 
| [...]
| C: RCPT TO:<ad@mpifr-bonn.mpg.de>
| S: 250 2.1.5 <ad@mpifr-bonn.mpg.de>... Recipient ok
| [...]

Maybe this is to be expected, sendmail thinks it is relaying and will
check if recipient domains are valid before accepting the recipient from an
upstream MTA.  This is desirable behaviour for relay, however message
submission is different.  (maybe this is why you had trouble with Nutscrape)
In message submission case it might be better for the submission
server accepted the recipient subject to stuff like a syntax check on the
recipient mailbox addresses and only validate them using DNS when flushing
the mail queue.  A non-delivery DSN (bounce) can be delivered to the sender
if the recipient domain cannot be resolved.

Unfortunately there seems to be no way to get sendmail to avoid the DNS
query in the RCPT command.  I'll investigate this a bit more - I was playing
about using telnet to sendmail and discovered this

C: XUSR
S: 250 Initial submission

I thought this might suppress the DNS, but no, it still does the query
on each RCPT command.  Using sendmail -U -bs via inetd doesnt help either :(
I'll see if I can find out what XUSR really does, I might need to add support
for it to libESMTP.

| Looks as if I now should try to fix the sendmail configuration, or better
| switch to something else, as you said before. Postfix, maybe? I just wonder
| why it worked before (and still if I use sendmail and balsa without libesmtp).

Well, a while ago I did ask the difference between execing sendmail in the
traditional way and using smtp.  I was told there was none except for
possible anti-spam checks.  Seems even the sendmail experts don't know what
it does!

If you do try another MTA, I'd look for one that actually supports
submission on 587 as distinct from relay on 25.  Meanwhile I'll have a look
at the feature list of a few MTAs I've messed with in the past.

| I guess I will *never* understand this program...

That's OK, nobody understands what it is that sendmail does from what I
can gather.

| Thanks a lot for your help!

:) 
Brian