Here is the log from my SMTP server (I am using hMailServer)
"SMTPD" 3784 5793 "2013-04-09 08:45:25.814" "<my ip addr>" "SENT: 220 domain.local"
"SMTPD" 3784 5793 "2013-04-09 08:45:25.814" "<my ip addr>" "RECEIVED: HELO MAILSVR"
"SMTPD" 3784 5793 "2013-04-09 08:45:25.814" "<my ip addr>" "SENT: 250 Hello."
"SMTPD" 3784 5793 "2013-04-09 08:45:25.814" "<my ip addr>" "RECEIVED: MAIL FROM: noreply@n"
"SMTPD" 3784 5793 "2013-04-09 08:45:25.829" "<my ip addr>" "SENT: 550 The address is not valid."

I also tried this in the agent config
*portCheck
DomainName = domain.local

The only diff
"SMTPD" 3784 5793 "2013-04-09 08:45:25.814" "<my ip addr>" "RECEIVED: MAIL FROM: noreply@d"

It appears the DomainName is truncated to 1 char