HTML Email Messed Up

Good Day,
I am having a problem with registration emails.  Out of the blue, with no change to the site, the email being sent to registrants are showing the actual HTML code instead of being sent in HTML format - I can't find any way to fix this - can someone help?

Thank You,

Jim 

Hmm

That's strange. Could be because mail client which you are using could not parse HTML email. Could you please ask someone else to try to see if they get similar issue?

Regards,

Tuan