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

Posted on 2007-11-28
Last Modified: 2013-12-17
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 .
Question by:ccfcfc
  • 3
  • 3
LVL 28

Expert Comment

by:Jan Springer
Comment Utility
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?

Author Comment

Comment Utility
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, []

LVL 28

Expert Comment

by:Jan Springer
Comment Utility
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?
Free book by J.Peter Bruzzese, Microsoft MVP

Are you using Office 365? Trying to set up email signatures but you’re struggling with transport rules and connectors? Let renowned Microsoft MVP J.Peter Bruzzese show you how in this exclusive e-book on Office 365 email signatures. Better yet, it’s free!


Author Comment

Comment Utility
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.

LVL 28

Accepted Solution

Jan Springer earned 250 total points
Comment Utility
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.

Author Closing Comment

Comment Utility
Thanks, removing the local domain fixed the problem. Kinda just needed confirmation of what I was thinking.

Featured Post

How to run any project with ease

Manage projects of all sizes how you want. Great for personal to-do lists, project milestones, team priorities and launch plans.
- Combine task lists, docs, spreadsheets, and chat in one
- View and edit from mobile/offline
- Cut down on emails

Join & Write a Comment

Nearly six years ago I was hired by a company to be their senior server engineer. One of my first projects was to implement Exchange Server 2007 on a Windows Server 2008 Single Copy Cluster for high availability. That was the easy part; read on to l…
Granting full access permission allows users to access mailboxes present in their database. By giving full access permission one can open and read the content of any mailbox but cannot send emails from that mailbox.
In this video we show how to create an Accepted Domain in Exchange 2013. We show this process by using the Exchange Admin Center. Log into Exchange Admin Center.: First we need to log into the Exchange Admin Center. Navigate to the Mail Flow >> Ac…
The basic steps you have just learned will be implemented in this video. The basic steps are shown to configure an Exchange DAG in a live working Exchange Server Environment and manage the same (Exchange Server 2010 Software is used in a Windows Ser…

743 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

18 Experts available now in Live!

Get 1:1 Help Now