MSGID_SPAM_CAPS fp's hitting messages from The Pension Regulator in UK

[Sebastian Arcus]

I'm not entirely sure what is the cause of this - notification emails 
from The Pension Regulator in UK (a government body overseeing pensions) 
have the destination email in upper case as part of the Message-ID. I 
don't know if the user has input their email address in caps when 
creating the account with TPR, and the system at TPR just preserves caps 
- or maybe their email software does that on purpose somehow. In all 
events, all email notifications from them go straight to the Junk 
folder. Do the standards really require a message id to be in all lower 
case?

I've enclosed one of the messages received here:
https://pastebin.com/9Bmu3pj1