Folks,
Looking at today's posts of GRC's Usenet I found a tool some of you may wanna try. The author also provides the full source code of the application. Following below, some of author's notes:
Wrote the tool quite some time ago for my personal needs, but since it may be useful for other people willing to run checks on SMTP servers and since it's useful for diagnostic purposes, I thought to share it, the zip file is available at this URL
http://www.mvps.org/bitbucket/smtptest.zip
and contains the 32 bits exe and the full "C" sources, the program is a simple commandline tool which may be used to perform some checks toward an SMTP server (or even the "FakeMX"), running the program without any arguments will show the following help
smtptest: simple SMTP server checking tool
Version 4.7 written by ObiWan Feb-2017
usage: smtptest [-option [value]] server_or_domain
option option meaning/usage
------------ ------------------------------------------
-p port SMTP port for connection (default=25)
-h helo HELO/EHLO string to use (default=DNS-PTR)
-e use HELO instead of EHLO
-a type AUTH type 1=PLAIN, 2=LOGIN
-U user AUTH user name
-P pass AUTH password
-x send a HELP command to the server
-f fromaddr use this address as the "from" (-c/-r)
-c address check <address> using VRFY/EXPN
-r recipient try an RCPT TO <recipient>
-M filename send an email from file contents
-t timeout connect/response timeout (default=10000)
-n retries number of retries on error (default=1)
-d delay delay between retries (default=30000)
-i ignore SMTP 5xx codes (keep going)
-T use TCP only for DNS queries (no UDP)
-I use ICMP to check if the host is alive
-m test all MX for the given domain
-C enable colors
-o dump traffic in readable format
-v enable verbose/debug logging mode
-? shows this help text
------------ ------------------------------------------
examples: smtptest mx1.hotmail.com
smtptest -t 30000 -v mx2.hotmail.com
smtptest -r postmaster@live.com mx3.hotmail.com
smtptest -xm hotmail.com
notice that while the program may optionally be used to send an email message, I purposely didn't optimize that part so hopefully it won't be abused as a "spam tool", also, the program currently doesn't support SSL, time ago I started fiddling with schannel code, but then I didn't go on and add it to the program, willing to do so, the best approach would probably be adding an "sslsock.c" module exposing the needed functions and then modifying the "smtptest.c" code to add calls to the module to deal with either implicit or explicit SSL modes.