The queue

Not everything happens at once. "Two days before the event" has to wait two days, and that waiting is done in the Queue tab.

The columns

ID, Action, Planned / executed, Attempts, Status.

Planned : Waiting for its moment.

Executed : Done.

Attempts counts retries. A message that failed once and then went through shows more than one.

What you can do

Retry runs a job again — useful after fixing an SMTP password. Delete drops it, alone or in bulk.

When nothing runs

The queue only moves if WordPress cron is running. If jobs pile up as Planned and their time has passed, that is the cause, and the dashboard says so at the top of the screen:

Background tasks are not running. 3 jobs are waiting — reminders and confirmation emails will not go out until this is fixed.

Settings → General settings → System information has Run tasks now to empty it by hand, and the fix itself is in Install and activate.

This is the single most common reason a confirmation email does not arrive. Check the queue before suspecting the mail server.