Sender reputation is a score assigned to an organization or person who is sending out emails.
Also referred to as sender score, it is determined by a number of factors, including the amount of email sent, bounced, opened, replied to, or forwarded as well as recipient complaints, etc.
Email sender reputation is a crucial aspect of email deliverability. The higher the reputation, the more likely your emails are to land in the inbox instead of the SPAM folder.
Email warm-up is a procedure for establishing a good sender reputation for a newly created account and increase its deliverability. This typically involves sending an increasing number of emails from this new account day after day - and making sure they are opened by the recipients.