My Send Emails Lands In My Customers' Spam / Junk folder

My Send Emails Lands In My Customers' Spam / Junk folder

Hi, 

I am having problems. It seems that all my emails that send out or replied, land in customers' spam/junk folder. 

I am losing opportunities here when 3 of my potential customers feedback that my emails were in their spam folder. 

Is there a way to rectify this ?