Various problems with the smtp module

[mikecardwell]

I've been experimenting with the "smtp" options with the "multiple" module.

[smtp]
trigger  = "smtp"
starttls = true
ehlo-domain = "example.com"
send-ehlo = true

There are three problems with the above:

1. I've explicitly had to tell it to send an EHLO rather than a HELO. Zgrab could just look at the initial welcome banner, and if it contains the string "ESMTP" it knows it should use EHLO rather than HELO. I don't think it should need specifying which to use, in the config file
2. I've told it to use STARTTLS. But I don't know if that is available in advance of running the scan. Zgrab will know if it's available as it will be able to check for it in the list of extensions if an EHLO is sent
3. I'm sending a string of the format ip,hostname,smtp,25 to zgrab's stdin. It would be good if zgrab used that hostname for the EHLO/HELO rather than having to specify it in the config file.

I am happy to contribute patches if we can agree on which (if any) of the above changes should be made, and how the config options should be changed.