LMTP error after end of data: 554 5.6.0 Message contains invalid header

[Michael Evans]

Cyrus is unable to receive some 8bit mime messages from MS Outlook 2016 and/or modern Apple / other mobile clients.

They are rejected with this error message (it would REALLY be nice if an extra patch also added /what/ header and octet offset the issue was from).

LMTP error after end of data: 554 5.6.0 Message contains invalid header

This page seems to indicate that the issue might have a resolution in the 3.0.x stable release of cyrus-imapd:

https://www.cyrusimap.org/imap/reference/faqs/interop-8bit.html

System information not included above:

Description: Ubuntu 18.04.1 LTS
Release: 18.04

cyrus-common:
  Installed: 2.5.10-3ubuntu1
  Candidate: 2.5.10-3ubuntu1
  Version table:
 *** 2.5.10-3ubuntu1 500

I have tried disabling 8bit mime support in exim4 as well, but it seems to be insufficient to resolve this issue.