I live in Japan where addresses routinely run longer than five lines. In
addition anything I send to the US usually requires more than five lines.

When using Envelopes and Mailing tab, I can highlight as many lines as I
like, but MS only prints out the first 5.

If that's what you insist on, fine. But tell me that by not allowing me to
highlight more than five lines for the address or sending up a warning box.