Okay, so using everyone’s comments as a starting point I came up with this silly mess 🙂 …
{
sleep 5;
echo 'ehlo';
sleep 3;
echo 'MAIL FROM:<Test@test.com>';
sleep 3;
echo 'RCPT TO: <kyle@test_dest.com>';
sleep 3;
echo 'DATA';
sleep 3;
echo -e 'To:kyle@testdest.com\nMIME-Version: 1.0 (mime-construct 1.9)\nContent-Type: application/zip\nContent-Transfer-Encoding: base64\n\n';
dd if=/dev/urandom bs=4 count=10 2>/dev/null | openssl base64;
echo '.';
} | telnet mx1.testdest.com 25