Are UTF-8 byte order marks in non-HTML emails ever legit?

Our spam appliance is letting a bunch of text-based phishing emails through. (We're getting another appliance...)

 

The emails have [byte order marks](https://en.wikipedia.org/wiki/Byte_order_mark), which I've just learned are invisible UTF-8 characters. In the emails we're getting, they look like =EF, =BB, =BF; they're randomly inserted in the body.

 

Is there ever a legitimate reason for these in email? Because our appliance isn't catching these, I'd like to write a pattern matching filter to just drop all emails that have …

cybersecurity emails html non order