Hotmail - Do they know I read their message?

Hi All,

I hope this is the right place to ask.

A while back an old friend sent me an email, from their hotmail address to my hotmail address. They apparently sent the email on their iPhone, as it was stated at the end of their email, and I read the email on my laptop. I didn't respond but now wish to make contact. Can they know that I read their email? I don't think you can with normal hotmail but I was wondering if there is the possibility of something on their iPhone that would let them know. I receive dozens of emails each day so I'm hoping I can just say I must have missed it.

Any assistance is warmly appreciated.

Lyb.