Email notification sent to some, not all recipients

I know there are a lot of posts about similar problems but none have solved my issue. Most of my forms send a notification to multiple recipients. I just separate the addresses with commas and it works. 

However, several of my forms are not sending to a specific address. The list looks like sxxx5@gmail.com,rxxxxxxs@totalenergysystems.com,cxxxk@mm-co.com,nxxxxl@totalenergysystems.com. When the notification email arrives, it only shows sxxx5@gmail.com,cxxxk@mm-co.com,nxxxxl@totalenergysystems.com in the TO field so it is not sending to rxxxxxxs@totalenergysystems.com for some reason.

I have tried putting that address in a separate notification email but that doesn't work either. I think the email is an alias and not a real email box but it is a client's email so I do not have access to it. Does the responder do any sort of checks to determine the validity of an email address? That's the only thing I can think of that might cause this.

I just reviewed the email r****s@totalenergysystems.com. It seems that it was in our bounce list because:

I have removed it from this list and you should be able to receive emails properly. If you are still experiencing this issue, you may verify if the email is in the list again from your account page:

How to remove your email address from bounce list

Please let us know if you require further assistance.