<mark> html tag not working in Send SMTP mail message activity

Dear Team,

I wanted to highlight some content in the mail body (to be sent via send smtp mail message activity).
I used <mark>text to higlight</mark> to perform the same. but it is not working.
All other html tags are working fine except <mark>

Eg : <html> This is my mail body.<mark>Text to highlight is here</mark></html>

is following ensured?
grafik

@ppr :It is already checked. All other html tags are working fine except

maybe mark tag is unclear supported. Give a try on rewrite it to:
<span style="background-color:yellow; color:black;">Highlighted text!!</span>

feel free to customize it as by your needs

Also have a look here: