if you were a retired teacher and someone you had as a student 25 years ago were to write you a 2-paged angry letter on how horribly you treated him And he left his name under the closing and his return address on the upper left hand corner of the envelop
No. Only someone with serious mental problems would write such a letter in the first place. I would be tempted to give it to the police out of fear of being stalked.
Nope. There's no value in responding to a complaint about something that happened 25 years ago. Nothing i could say would make the last quarter century different for that person, even if i felt their accusations held any merit.