Question : 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 @hotmail.com or @gmail.com  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 It is really weird as to why we are unable to send to every other domain than our own.
Appreciate as to why .

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

No, all you have to do is remove 'intamac.com' from /etc/mail/local-host-names and restart sendmail.

You would leave in 'mail01.intamac.com' 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 intamac.com, then there is nothing else to do.  If it does not, then we need to fix DNS.