If that’s the case I misread the initial request but still you can use the flows mentioned with countdown to send based on the trigger .
Or if the mail sensor is only triggered when specifically doing something in the mail box you can say;
Flow 1;
When image is grabbed
AND mailbox sensor is triggered
THEN send “you’ve got mail”
Flow 2;
When image is grabbed
AND mailbox sensor is NOT triggered
THEN send “someone at the door”