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sendmail and HELO command

Fabio Ettore
Honored Contributor

sendmail and HELO command

Good morning everybody,

a question about sendmail.
I would like to do sendmail works with HELO command like the following: normally sendmail sends an HELO command with the hostname

HELO pippo.
or with FQDN
HELO pippo.pluto.com

Now I would like to send the HELO command with the IP address, e.g.

HELO 13.14.15.16

I would like that because this hostname is not recognized from any DNS and SMTP server doesn't recognize it as well. It is recognized by the IP address.
Surely a possible solution should be to solve it by DNS correctly but btw I would like to know if what I am asing is possible.

All replies will be appreciated.

Thanks and regards,
Fabio
WISH? IMPROVEMENT!
8 REPLIES
Bill Hassell
Honored Contributor

Re: sendmail and HELO command

Add the IP address and a name for this system into the hosts and sendmail.cw files. Then edit nsswitch.conf to use files then dns for hostname resolution (the default is dns then files).


Bill Hassell, sysadmin
Fabio Ettore
Honored Contributor

Re: sendmail and HELO command

Hi Bill,

this system doesn't use DNS, just /etc/hosts.
For that I have already configured /etc/nsswitch.conf to see only the files

hosts: files

but not sendmail.cw. I have just configured it now sendmail.cw contains

13.14.15.16
localhost
pluto

and then sendmail stop/start.... but it still fails searching for hostname

>>> EHLO pluto.
....
504 : Sender address rejected: need fully-qualified address
Service unavailable

Thx anyway Bill.

Other hints would be appreciated as well.

Regards,
Fabio

Thanks anyway
WISH? IMPROVEMENT!
Geoff Wild
Honored Contributor

Re: sendmail and HELO command

Put the FQDN in your /etc/hosts and give that a try...

Rgds...Geoff
Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.
Fabio Ettore
Honored Contributor

Re: sendmail and HELO command

Hi Geoff,

tried that....in /etc/hosts

13.14.15.16 pippo pippo.pluto.it

but it is failing yet with

Deferred: 450 : Sender address rejected: Domain not found

In my previous post I wrote pluto like hostname..not consider it since the hostname is pippo, so s/pluto/pippo in my previous post.

Thanks anyway Geoff.

Other hints appreciated.

Regards,
Fabio
WISH? IMPROVEMENT!
Geoff Wild
Honored Contributor

Re: sendmail and HELO command

What about trying masquerading?

Set the DM macro to yourdomain.com in sendmail.cf:

DMpluto.com

Rgds...Geoff
Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.
Sameer_Nirmal
Honored Contributor

Re: sendmail and HELO command

Hi,

As far as your question about using IP address instead of hostname for HELO or EHELO
is NOT possible.

Since Sendmail 8.1.7 as per RFC 1123 which stipulates 'HELO' and 'EHELO' commands are
followed by a fully qualified hostname.
The same is confirmed by the error 504 in your case.

There has to be aresolved host-name in FQDN form to make sendmail work. The resolution may be from /etc/hosts or DNS , but it has to be there.
Christopher Caldwell
Honored Contributor

Re: sendmail and HELO command

I don't recommend following the hack I'm about to give you, because your stated issue points to a problem that should be fixed via DNS or /etc/hosts.

If you can nslookup domain_name at the command prompt, then sendmail should be able to as well, and your problem would be solved.

The sendmail guys put in most of the HELO checks to minimize spam and hacking attempts, so the following advice circuments those controls, thus potentially opening you up to spam, hacks, and other bad behavior:

Try changing this line to
#O AllowBogusHELO=False
O AllowBogusHELO=True
in sendmail.cf. Restart sendmail.


Fabio Ettore
Honored Contributor

Re: sendmail and HELO command

thanks
WISH? IMPROVEMENT!