My Outgoing Email doesn't always reach everyone

About 50% of my outgoing emails are not going through to the recipients. I not sure which one's are received or not because I am not getting a message back saying the email did not connect. I accidently find out when someone emails over again. I just want
Joan Mohr
Helga
Alison
Dawn
and Kathie Koulouris

I did receive your emails either yesterday or today.

Sheila