Sorry to suggest a non-perl solution, but given that you have a web server capable of supporting an SMTP server, here's a simpler possibility:

Juno is no doubt just filtering port 25. You can set sendmail to listen on some other port which isn't filtered by Juno, then set your email client to connect to that port instead of the standard SMTP port.

In fact, port 587 has been designated as the standard port for this kind of operation (see RFC 2476). You should find some mention of the "message submission protocol" in the sendmail documentation.