SMTP probe issue

Has anyone created their own smtp probe before?
I wish to monitor smtp (sendmail) on a few servers. However, I noticed while testing the default smtp probe; While it did show smtp server functionality (green). It also showed green for various other machines which did not have an smtp service running on them.

Has anyone experienced this before? Has anyone created a more advanced test?

I’m not able to get green SMTP, where such service is not enabled, I’m using default SMTP probe on Dude v3.2.
If you are not satisfied with default SMTP probe, it is possible to create more advanced SMTP probe and check much more details, then it is with default one.