I guess it depends most on what the future might bring. This works but you won't be able to carry everything to a winbox and expect it to run there. With MIME::Lite you got a much better chance at that.
Another question you may ask yourself is: ,,What if someone else has to go into my code''. With ,,mail'' you expect that person to also understand something about linux, where the MIME::Lite path would only require someone to know all about perl. ;)
And then the third, if you're supposed to use MIME::Lite... I guess you're supposed to use MIME::Lite.