Is there a way for my script to know which "mailing" system is on a server?

Besides asking your system administrator as Abigail suggests you could open a socket to port 25 on the machine in question, see if something answers and look at the banner. Sendmail (for instance) depending on how your SysAdmn has configured it will give you something like:

]$ telnet localhost 25
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
220 myhost.com ESMTP Sendmail 8.12.5/8.12.5; Tue, 2 Sep 2003 12:02:58 
+-0400
[download]

Keep in mind some folks modify the sendmail.cf file to obfuscate the fact that sendmail is running on the host as well as which version of sendmail. YMMV.

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Peter L. Berghold -- Unix Professional Peter at Berghold dot Net
	Dog trainer, dog agility exhibitor, brewer of fine Belgian style ales. Happiness is a warm, tired, contented dog curled up at your side and a good Belgian ale in your chalice.