With Soapbox Mailer, you can have multiple sender email addresses from up to 1,000 different domains! Most organizations likely will only have one domain they'll want to use, but in case you want to send from multiple domains, please follow the steps listed in the following guide from Amazon Simple Email Services (SES) to verify your domains before you try to send any emails from Soapbox Mailer.
Verifying Domains In Amazon SES
Happy emailing!