Mail is being rejected with "Relaying denied" error on "ruleset=check_rcpt".
Jan 5 12:38:53 innofinity.com sendmail: i05HcfdX022496: ruleset=check_rcpt, arg1=, relay=[IP], reject=550 5.7.1 ... Relaying denied
This error may appear In case sendmail.cf file contains a line like the following:
# Resolve map (to check if a host exists in check_mail) Kresolve host -a -T
explanation about this issue can be found at www.sendmail.org/ftp/KNOWNBUGS:
"Sender addresses whose domain part cause a temporary A record lookup failure but have a valid MX record will be temporarily rejected in the default configuration."