Whatever the reason, I don't see why it was possible to open normally on the laptop, but not the desktop or iPad ?
Theoretically I agree, emails generally should/will open consistently on all devices. Even more so given your description of the nature of the emails.
What makes your problem all the more interesting is that its occurring on different computer platforms too along with different email software.
But without seeing the raw source of the mail its a little difficult and would be effectively a needle in a haystack job.
I hadn't sent it all in capitals and the other recipients received it normally, as sent.
Why would this happen?
Has he been receiving other mails like that, or just yours ? Is it consistent for you, or just that one ?