1. Click on 'API Integrations' on the left hand side of the MXT menu, select 'Email Settings'.
2. Under 'Allowed sender email addresses' insert the email addresses that you are allowing Email to SMS to be sent from.
For example: firstname.lastname@example.org
Note: When adding multiple emails these will have to be separated and inserted onto new individual lines.
3. Click on 'update settings' to save these changes.
To add a catch-all (wildcard) email address domain to 'Allowed sender email addresses', please see: Email Domain Whitelist for Email to SMS Allowed Senders.