Sender reputation is a rating that email mailbox providers keep for every sending domain and server address. It determines whether a message ends up in the inbox, in the spam folder, or is not delivered at all. It is shaped mainly by the share of messages marked as spam, the share of non-existent addresses, the rate of opens and interactions, the stability of sending volume, and the technical setup of sender authentication. It can be damaged quickly by a single ill-judged campaign, while repairing it takes weeks to months. Recovery proceeds by reducing volume, sending only to the most active contacts, and gradually expanding, which rebuilds the reputation from scratch. It is therefore worth monitoring the tools providers offer that show a domain's status, and reacting before a problem shows up.
See also: Email Deliverability, Contact import.
