What is "sender reputation"?
Every time you send an email the internet service provider (Gmail, Microsoft, Yahoo ect), uses a reputation score about your email account and domain to decide if your email should be delivered and then which folder it should be delivered to.
This score is based on how other users of their system (other Gmail or Microsoft email accounts) have interacted with your emails in the past, as well as the content of your email playing a part.
If the score bad (low numbers of replies from users, very rarely have messages marked as important and spammy content), your email will either land in the spam/promotions folder or not be delivered (bounce due to rejection). Eventually, your account can get suspend if this gets very bad.
When your score is good (lots of people reply to your emails, mark them as important and the content looks genuine), your emails will be delivered to the priority inbox. Therefore, you will get a higher response rate as your emails can be read by the decision-makers you want to pitch.