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Issue with sendmail DS and MX records

Marc Riley
Occasional Contributor

Issue with sendmail DS and MX records

Hi there,

Have a query on sendmail that has been annoying me for a little while now, as I can not seem to find the exact answer I am looking for.

We have several hpux hosts that when configured to use DNS, will ignore the DS (smart relay) macro and rely purely on MX records for relaying. This is causing us issues at the moment, as our customer has migrated their DNS to a Win2K/Active Directory solution, which has broken the MX records that were setup specifically for mail, and have said that they can not replicate it in this new solution.

I have found that you can "trick" sendmail into ignoring DNS altogether (change F=mDFMuX to F=0mDFMuX and remove rule to make hostname canonical), but this apparently breaks RFC's, and also causes issues with incoming email.

Is anyone else aware of this issue of the DS not working when the client uses DNS, as I hadn't come across the problem before? I could provide a lot more detail, but trying to keep it simple to start with.

Berlene Herren
Honored Contributor

Re: Issue with sendmail DS and MX records

Morning, Marc
There are a couple of things to try:

Put the mail relay in brackets, like so


Recycle sendmail

If that doesn't work, use the IP address, again in brackets.

You can also try commenting out this line:

# pass to name server to make hostname canonical
# R$* < @ $* $~P > $* $: $1 < @ $[ $2 $3 $] > $4

Hope one of these works,
Steve Post
Trusted Contributor

Re: Issue with sendmail DS and MX records

I had a problem where the DNS would not match the actual ip address because the box in in-between the outside (internet), and inside lan.

I asked for help here and via hp support got an answer good enough to work.

Use the DS line with Square Brackets. I have been told this bypasses DNS. I know it works because my the ip address of the mail server from this box is completely different from DNS.


Now I suppose you can use /etc/hosts and /etc/resolv.conf and /etc/nsswitch.conf. But I didn't. Not for this. Whenever I tried using DNS, email ignored all and went straight to whatever the MX record said.