Verify forwarding addresses
Gmail enables users to automatically forward incoming mail to another email address. A user can forward all of his or her incoming mail or create a filter that forwards just the mail that meets specific criteria.
To ensure that the user is forwarding mail to a legitimate recipient, Gmail requires the user to verify the email address. When the user adds a forwarding address, Gmail sends an email message to the address asking the recipient to affirm that the user is allowed to forward mail to that address. (Learn more about the process.)
For G Suite and Education customers, Gmail does not require the user to verify the forwarding address if the email address is for a user or group in your organization; that is, if the address is in a domain that is registered as part of your G Suite account.