Why is my email blast only reaching 20% of my list?

[Well-Lox]

Hello,

When I send out an email blast. Your system only sends out 20% of my emails.  

Why is this happening? Is the format of my email list not right?

Can I export my list and clean it up then import the list again?

Your experts were not helpful at all. No one was available or interested in this type of job

This is becoming a problem

Thank you