> What is the legitimate reason to use base64 encoded emails ?

i see quite a lot of legitimate email as base64 encoded

> Seems to me, it is only being used by spammers to complicate
> body_checks

any modern checker can and will decode base64 or indeed other message
details (the cost of doing so is quite low)

> Would it be crazy to want to configure Postfix to not accept base64?

that will break a lot of legitimate sources