One cool way to check your email routing
I've been getting a strange "User unknown" error from sendmail today, when everything should have worked fine and even though users did exist. Here's some info on the problem's source and solution.
We have a domain called "talentnavi.biz", and I was asked to add a new subdomain to that domain ("kansai.talentnavi.biz"), and add new email addresses for several users who will be using that domain. I have setup everything properly on the server site by adding users and updating local domains and virtusers lists, however, when I was trying to test the delivery of the messages, I was getting "User unknown" errors and my emails to the newly-created mailboxes were bounced back.
I checked my mail server's logs, but there were of no help at all. After some googling, I found a very nice solution! In order to see how an email to a particular email address gets delivered, you should run the following command as root:
sendmail -d60.5 -d27.2 -bv info@example.com
So, in my case the command and output were as follows:
[root@me-ja mike]# sendmail -d60.5 -d27.2 -bv info@kansai.talentnavi.biz
map_lookup(dequote, mike, %0=mike) => NOT FOUND (0)
map_lookup(host, kansai.talentnavi.biz, %0=kansai.talentnavi.biz) => talentnavi.biz. (0)
map_lookup(dequote, info, %0=info) => NOT FOUND (0)
map_lookup(virtuser, info@talentnavi.biz, %0=info@talentnavi.biz, %1=info) => NOT FOUND (0)
map_lookup(virtuser, @talentnavi.biz, %0=@talentnavi.biz, %1=info) => NOT FOUND (0)
alias(info)
info@kansai.talentnavi.biz… User unknown
So, turns out that I have incorrectly configured my DNS records. They were set up like the following:
talentnavi.biz A 123.123.123.123
talentnavi.biz MX talentnavi.biz
kansai.talentnavi.biz CNAME talentnavi.biz
So, by default, the kansai.talentnavi.biz was aliased to talentnavi.biz, and since I didn't have a separate MX record for kansai.talentnavi.biz, the talentnavi.biz was used for mail delivery.
mike-meja:~ mike$ host -t mx kansai.talentnavi.biz
kansai.talentnavi.biz is an alias for talentnavi.biz.
talentnavi.biz mail is handled by 20 talentnavi.biz.
Therefore, the all email which was sent to "info@kansai.talentnavi.biz", was actually attempted to be delivered to "info@talentnavi.biz", because there was no separate MX record for the kansai. subdomain.
The solution is of course to add :
kansai.talentnavi.biz MX kansai.talentnavi.biz
Record to DNS server, and everything should work fine.