When you tap Send, the message leaves your device and is stored on mail servers and possibly on the recipient’s device, which is what makes it ‘sent.
If you delete an email from your Sent folder or your local client, the message has already been delivered to the remote server and to the recipient, so the sending event itself is not undone. Deletion typically removes local copies and hides the message from your view, but copies can remain on servers, in backups, or on the recipient’s device depending on retention settings and sync behavior. This evergreen status and relationship clarification explains what persists, what changes, and how to interpret ‘sent’ after deletion.