When I want to check a mail server with service="SMTP" OpenNMS keeps telling me that the service is down "Did not receive expected response within timeout timeout". I traced the problem and saw, that OpenNMS stop the communication after the first answer of the SMTP server.
On my server the first answer ist "220-ESMTP ..." and a CR.
After 3 seconds postfix continues with a "220 ESMTP ..." and CRLF.
According to the RFC clients have to wait until the CRLF is sent. OpenNMS does not wait. So it sees the wrong banner.
I have to reconfigure my postfix to make an exeption for my opennms server and to deliver the correct banner from the start.
I would be nice, if the problem could be fixed within OpenNMS.