Neither the Sender ID nor the DomainKey setting is mandatory. However, they directly influence the delivery of your campaigns and classify your emails as free of spam.
The Sender ID is an authorization that allows you to send emails on your behalf. This option is available on DNS server of your domain. In emailmanager, all your campaigns are recognized as free of spam, as they are sent from different servers.
The DomainKey is an e-mail authorization system designed to verify the DNS domain of an e-mail sender. All e-mails sent by means of our online tool have this "key” in the message header, which allows the destination server to verify the DNS value of your e-mail.
Hotmail, Gmail, and Yahoo servers use these authenticators. Therefore, these settings are essential to achieve solid results with your campaigns.