The mail that carries a student-number linking link. Every placeholder comes from the delivery
row because the recipient may have no account here, and the “you received this because” line has
to stay because the message is unsolicited. A migration cannot insert a row using an enum value
it adds itself, so in dev and tests these templates come only from here.
Told to a student whose student number we linked from a matching verified email address, without
them clicking anything. A compensating control for that automatic link: it is how someone finds
out a number was attached to their account and can detach it.