Many of my emails are not being received by my customers. Is there any way to fix this? I called customer support a couple weeks ago.

Many of my emails are not being received by my customers and will also sometimes have a long lag of hours or a day before it is received. I've confirmed the email are not sitting in my outbox. Is there any way to fix this? I called customer support a couple weeks ago and was informed a ticket would be opened and someone would get back in touch with me. I have yet to have any followup and continue to have the same problem with emails. The email address that is continuously having issues is chris@placemakerdesignstudio.com .