I just set this up (*) and tried to send email via the sendmail running on my FreeBSD server. I got this:
2020-11-16 10:53:50.400 am [debug](http://hubitat-hub/device/edit/385)lastCommand = helo
2020-11-16 10:53:50.396 am [debug](http://hubitat-hub/device/edit/385)In parse - 501 5.0.0 helo requires domain address
Sure enough, you are sending HELO without a hostname, and sendmail rejects that by default.
I changed line 101 to this and worked around it (it requires a hostname, but it doesn't check the value).
def res1 = sendData("helo hubitat",500)
(*) You might add this instruction to the first post:
After adding this under Drivers Code (or using HPM), under Devices use "Add Virtual Device" and select this driver under "Type".
