Mail.td is a receive-only service. You can receive emails at your temp mail address, but you cannot send emails from it.
Why no sending?
Outbound email requires a trusted sending reputation. Shared sending infrastructure is quickly flagged as spam, which would make any emails sent from Mail.td unreliable or undeliverable. To keep inbound delivery fast and reliable, Mail.td focuses on receiving only.
If you need to send emails
Use a dedicated email provider (Gmail, Outlook, or a transactional email service like SendGrid or AWS SES) for any outbound communication.