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reject = 501 Sender domain must exist


reject = 501 Sender domain must exist

I'm configuring sendmail to be able to send email to Internet. My local domain has not been registered and got any public IP yet. I'm not able to send the email to outsite. In mail.log, there is an error "ruleset=check_mail, arg1=, [], reject=501 Sender domain must exist" It seems my domain cannot be resolved. However, in /etc/hosts. I alredy define domain name as
" hostname"
What else should I check?
Marcel Boogert_1
Trusted Contributor

Re: reject = 501 Sender domain must exist

Hi there,

Try the following and reply with the output:

$ sendmail -v

Regards, MB.
Honored Contributor

Re: reject = 501 Sender domain must exist

It is because of /etc/hosts and hostname resolvation there.

Try to change as, hostname

--- /etc/nsswitch.conf ---

hosts: files dns


Try nslookup now.

And your will work now.
Easy to suggest when don't know about the problem!