Hi @bmoore,
As you can see in the 'cat -v -e' command output, line break will be shown as '^M$', but your mail body doesn't have line breaks at all. I suggest you contact your application provider for a potential solution (i don't mean it's their issue, just a potential opportunity).
P.S. You modified many Postfix settings which i think it's bad idea. But i don't know your requirements, so it's fine if you understand what you're doing.
smtpd_helo_required
smtpd_recipient_restrictions
smtpd_reject_unlisted_sender
smtpd_sasl_local_domain