A whitelist, also called an allowlist, is a list of approved email addresses, domains, or IP addresses that an email system recognizes as trusted. Depending on how the system is configured, messages from approved senders may be allowed through certain filtering rules instead of being treated like unrecognized or unwanted email.
How Does Email Whitelisting Work?
When an email arrives, the receiving system compares information about the sender with its configured allowlist. If the sender matches an approved address, domain, or IP address, the system may apply different filtering rules to that message.
The exact behavior depends on the mail server, email client, or security gateway. Some systems use whitelists as an explicit exception to filtering, while others combine allowlists with additional security and reputation checks.
What Can Be Whitelisted?
Email systems can allow different types of sender information, including:
-
Email addresses: A specific sender, such as
user@example.com. -
Domains: A domain, such as
example.com, allowing messages from approved addresses within that domain. - IP addresses: A specific sending IP address used by a mail server or email service.
The level at which an allowlist is applied depends on the receiving system and its configuration.
Does Whitelisting Guarantee Email Delivery?
Whitelisting can allow messages from an approved sender to bypass certain filtering rules within a particular email system. However, other factors, such as authentication , security policies, sender reputation , and recipient-side filtering, can still affect whether the message is delivered or reaches the inbox.