Sendmail error "lost input channel from" using Sendmail version 8.13.1

Using Sendmail version 8.13.1 from a Linux box.
Seem to be getting " lost input channel  "  and a "User Unknown " almost immediate. Can send email to every other external domains i.e or  but if the destination domain is the company's domain then it gets rejected.
This sendmail in on an internal network and allows mail out /in and due to other mail going out we know the firewall is not to blame for rejection. The mails being sent go via the correct SMTP server as seen in the mail log.
I have added a RELAY  to this domain and even SPAM CONTROL for that Domain to ALLOW . But every time we get "lost input channel" and almost immediately the <  user Unknown  then the   "lost input channel".
It is really weird as to why we are unable to send to every other domain than our own.
Appreciate as to why .
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Jan SpringerConnect With a Mentor Commented:
No, all you have to do is remove '' from /etc/mail/local-host-names and restart sendmail.

You would leave in '' for its own mail delivery unless you are forwarding that host's mail.

If mail01 can properly resolve DNS and get the MX records for, then there is nothing else to do.  If it does not, then we need to fix DNS.
Jan SpringerCommented:
What do you get when you telnet to port 25 of the machine hosting your domain?

Does your sendmail box think that your domain is local to that machine (/etc/mail/local-host-names)?

Is the MX record for your domain pointing to the correct fully qualified domain name?

Could you post the /var/log/maillog snippet?
ccfcfcAuthor Commented:
Emails go out as you can see below so I know SMTP traffic is working. The MX record works and is valid as it is used for company emails in general. SO I know the Domain/MX is correct

See extract from maillog , hope this helps
This one worked - see destination address :-
from=<>, size=639, class=0, nrcpts=1, msgid=<>, proto=ESMTP, daemon=Daemon0, []
Nov 28 11:47:18 mail01 sendmail[11403]: lASBlHEw011401: to=<>, delay=00:00:01, xdelay=00:00:01, mailer=relay, pri=120639, [], dsn=2.0.0, stat=Sent (OK id=1IxLLu-0005Is-M1)

This one not - same application creating email . For some reason it tried to use different SMTP agent
<>... User unknown
Nov 28 12:11:05 mail01 sendmail[11532]: lASCB53r011532: lost input channel from [] to Daemon0 after rcpt
Nov 28 12:11:05 mail01 sendmail[11532]: lASCB53r011532: from=<>, size=0, class=0, nrcpts=0, proto=ESMTP, daemon=Daemon0, []
Nov 28 12:12:10 mail01 sendmail[11550]: lASCC9gd011550: <>... User unknown
Nov 28 12:12:10 mail01 sendmail[11550]: lASCC9gd011550: lost input channel from [] to Daemon0 after rcpt
Nov 28 12:12:10 mail01 sendmail[11550]: lASCC9gd011550: from=<>, size=0, class=0, nrcpts=0, proto=ESMTP, daemon=Daemon0, []

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Jan SpringerCommented:
Does mail01 /etc/mail/local-host-names have ''?

If so, are the mailboxes on mail01?

Is it possible that mail01 is trying to deliver the mail locally and shouldn't?
ccfcfcAuthor Commented:
Yes /etc /mail/local-host-names does have in it.
No the mail boxes are not on mail01 but on an external domain used by the company.
Well I kinda guessed that mail01 was trying to do that but and should not as the username for the domain are external. Whats is confusing if we sent to any other domain they get sent as expected.
Like I said I have added SPAN CONTROL entry and a relay entry to allow to go to . It is as you said, it is trying to deliver to the local mail01 server of which the require dmailbox does not exist on.
I guess I need to force mail out if it says  <usrename> . Not entirely sure as to why is this not happening already.

ccfcfcAuthor Commented:
Thanks, removing the local domain fixed the problem. Kinda just needed confirmation of what I was thinking.
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