Hello,
Can someone help interpret this error?

Last error: 5.0.0 554 Failed: Malformed MIME field: Comments:
                            RFC822 error: <W> Invalid RFC822 field - 
[0xC2] ...

I recently added templates for BOTTOM_BANNER and BOTTOM_BANNER_HTML to a 
list that I manage. Some HTML messages were distributed today, and the 
bottom banner appeared to be working fine ... but then and the error 
monitoring report came in with this same error for about 18 addresses - 
most coming from two distinct email hosts.
Is this something that subscribers need to correct with their email 
provider?

Thanks in advance for any help,
  -Birdie