Is this sentence not implying that it is the son's father?

A son will send the dad a letter should also be accepted.

The English wording is too specific here. It should accept more options like "his dad" or changing the word order: "The son will send his dad a letter"

This should be a lot more lenient; it is clearly natural to assume that we're clear to use sentences such as "the son will send his dad a letter", like it has been discussed before myself. Also, is the English translation just kinda awkward or is that just me?

Any reason why the verb is 보내주다 here? What is the difference between 보내주다 and 보내다?

Edit: Answering my own question. It has 아/어주다 because the son is doing something for the dad.

Korean grammar is messing up my English grammar. I put "A son will send to the dad a letter"