If you're making no assumptions other than having Perl installed, as some systems are shipped in a condition that can only be described as being both spartan and antiquated, then you've got the right idea.

If you're willing to allow for modules, you could use something like Mail::Sender.

It is quite trivial to write an SMTP application like that module, using IO::Socket to help you out. However, you will not get the same reliability as you would with /bin/mail, since you will have to handle your own retries.