To send your emails you have to add a sender email address or domain to your API key and validate it. You can do so from the Mailjet app or via the API.
In addition, you will need to modify your DNS records to include DKIM signature and SPF. This will help Inbox Service Providers (ISPs) and webmail servers (e.g. Gmail or Yahoo) verify that the emails are being sent from an authorized server. Once setup, SPF & DKIM will also help with your deliverability – meaning your emails have a better chance of being delivered to the recipient’s inbox and not their spam folder.
To create a new sending address for your API key, do a POST on the /sender resource.
In the payload set the value of Email to the respective address. To register an email domain, you can use a catch-all expression like *@yourdomain.com instead.
Whenever you register a sender, the domain name will be extracted from the email address and the system will create a dns entry for it. Do a GET on /dns/{dns_ID or dns_domain} to get the SPF, DKIM and sender validation information for this domain.