Supression of CNAME expansion in sendmail

[Alexander Yegorov]

Hi Sendmail community,

I have a necessity to supress expansion of CNAME record as domain portion of email address. Example:
domain.com IN CNAME ghs.some.other.domain.net.

As a result, when I am sending out using ema...@domain.com as from field, my MTA rewrites it through canonify ruleset (Canonify2 ruleset) to ema...@ghs.some.other.domain.net.

Need to supress that action.
After readings of sendmail book 4-th edition, no default mechanisms were found.

I have composed interim hack using additional class and addition into Canonify2 ruleset:


# file containing names of hosts,which should not be canonicalized at Canonify2 by $[ $]
F{skipcanonify}/etc/mail/skipcanonify

SCanonofy2=96
.....
# Domains, which are present in skipcanonify will not be canonified on purpose
R$* $| $* < @ $={skipcanonify} > $* $: $2 < @ $3 > $4
.....

cat /etc/mail/skipcanonify
domain.com




Still, it would be nice to know if there is some built in solution?
Would you please advise?

[Kees Theunissen]

Put a line near the top of your sendmail.mc file reading:
define(`confDONT_EXPAND_CNAMES',`True')dnl

But be aware that external servers still might expand the CNAME if:
a: you relay the message through an external server, or
b: you receive mail from external senders.

Servers used by external senders -and the configuration of those
servers- is completely out of your control so you can't rely on this
setting. To be safe the receiving server should be prepared to
accept mail for the expanded CNAME.


Regards,

Kees.

--
Kees Theunissen.

[Alexander Yegorov]

среда, 30 мая 2012 г., 21:05:33 UTC+3 пользователь Kees Theunissen написал:

Thank you for quick advise, Kees.
I realized that receiving server also should be aware about CNAM suppresion.

[l.soma...@gmail.com]

Hi Kees,

I need help from you. I have one linux domain.
Domain name is actaul.domain.net and i have created the Cname as soma.sekhar.net.
When i sent mail from my out look to mai...@actaul.domain.net the mails are delivering to the server.
but when i sent a mail to mai...@soma.sekhar.net (it is cname) the mails are bouncing back to my from mail id.
in the linux maillog i am able to see the below error?
dsn=5.1.1, stat=User unknown
DSN: User unknown

Can you please help me. how to configure the sendmailconfiguration for the cname mails.

[Kees Theunissen]

l.soma...@gmail.com wrote:

> Hi Kees,
>
> I need help from you. I have one linux domain.
> Domain name is actaul.domain.net and i have created the Cname as soma.sekhar.net.
> When i sent mail from my out look to mai...@actaul.domain.net the mails are delivering to the server.
> but when i sent a mail to mai...@soma.sekhar.net (it is cname) the mails are bouncing back to my from mail id.
> in the linux maillog i am able to see the below error?
> dsn=5.1.1, stat=User unknown
> DSN: User unknown
>
> Can you please help me. how to configure the sendmailconfiguration for the cname mails.
>

The CNAME you mentioned doesn't seem to exist:

~$ dig soma.sekhar.net

; <<>> DiG 9.9.4-P2 <<>> soma.sekhar.net
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 4241
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;soma.sekhar.net. IN A

;; AUTHORITY SECTION:
sekhar.net. 3241 IN SOA ns03.domaincontrol.com. dns.jomax.net.
2013012900 28800 7200 604800 3600

;; Query time: 10 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Tue Mar 25 01:59:43 CET 2014
;; MSG SIZE rcvd: 112


So I guess you should start fixing that.

[l.soma...@gmail.com]

Hi Kees,

Yes. Your are correct. soma.sekhar.net is an example. as per security reasons i have not provided the actual cname what i used. here my issue is,
The sendmail is not able to receive the mails with cname.
I have 2 scenarios.
1. Sending a mail to the actual DNS name- It is working now.
2. Sending a mail with Cname to the same server(point1). it is failing.
Can i know the configurations in the sendmail.cf or sendmail.mc/
how to configure the cname?