An email, which includes a header and historical information, is created. The header comprises a destination email address, which comprises a name of an addressed recipient of the email and a domain name of the destination email address. The historical information in the email comprises an approved address for a previously exchanged email with the addressed recipient. The first approved address is compared to a corresponding portion of the first destination email address. In response to the corresponding portion of the first destination email address being different from the first approved address as stored in the storage unit, a warning is outputted. The warning comprises both the approved address, and an unapproved address list that comprises the first destination email address.