Here is an example of an evaluation-time Safe-Tcl script: it is executed whenever the user views the message that contains this script.
From rutger Mon May 30 11:19:01 1994
Received: by arrakis.home.com (Smail3.1.28.1 #6)
	id m0q85Mz-0006T2C; Mon, 30 May 94 11:19 GMT
Date: Mon, 30 May 94 11:19 GMT
From: rutger
MIME-Version: 1.0
To: frodo
Subject: MIME op de KUB
Message-ID: <406_127_770296739_1@arrakis>
Content-type: multipart/mixed;
	boundary="PART.BOUNDARY.406.127.arrakis.770296739.1"
Status: RO

--PART.BOUNDARY.406.127.arrakis.770296739.1
Content-ID: <406_127_770296739_2@arrakis>
Content-type: application/safe-tcl

proc mime_lobby {} {
    set myname [SafeTcl_getconfigdata  "username" "" \
                "Your name, please: "]
    SafeTcl_sendmessage  -to rekencentrum@kub.nl \
            -subject "MIME at Tilburg University" \
            -body [SafeTcl_makebody "text/plain" \
"I would like to ask your organization to extend the recent implemented
electronic mail and news facilities with Multi-purpose Internet Mail
Extensions (MIME).

Regards,
$myname"]
exit
} if {[lsearch $SafeTcl_InterfaceStyle Tk3.*] >= 0} {
    set foo [mkwindow]
    message $foo.m -aspect 1000 \
       -text "Click:"
    button $foo.b1 \
       -text "Here if you want to be able to use MIME." \
       -command {mime_lobby}
    button $foo.b2 \
       -text "Here if you want to quit without taking any action." \
       -command exit
    pack append $foo $foo.m {pady 20} \
                $foo.b1 {pady 20} \
                $foo.b2 {pady 20}
} else {
    set ans1 [string index [SafeTcl_getline \
    "Do you wish MIME (Yes/No)?" "Nee"] 0]
    if {$ans1 == "Y" || $ans1 == "y"} {
        mime_lobby
    }
    exit
}
--PART.BOUNDARY.406.127.arrakis.770296739.1--

Below you can find the result if this script is evaluated in an X windows system.