SMTP credentials are the username, password, API token, or other login material used to authenticate to a mail server or email delivery service over the Simple Mail Transfer Protocol (SMTP). They let approved systems send messages on behalf of an organization, such as alerts, password resets, invoices, and security notifications.
These credentials matter because exposed mail access can be abused to send spam or phishing, impersonate trusted internal systems, and interfere with alerting and account recovery workflows. In real attacks, threat actors often seek SMTP credentials alongside cloud keys or other secrets because a working mail account can help them hide activity, confirm access, or pivot into broader compromise. Defenders should store them securely, restrict who can use them, monitor outbound mail patterns, and rotate them quickly if leakage is suspected.