How do I schedule an email to send later?

In the composer, choose Schedule send / Send later and pick a time — Later Today, This Evening, Tomorrow Morning, Tomorrow Afternoon, Next Week, This Weekend, or Pick date & time.

To stop it, open the scheduled message and choose Cancel send / Edit as draft — Cancel the scheduled send and edit as a draft. Omega confirms Send cancelled.

Scheduled sends cannot carry attachments — you will see Can't schedule with attachments.