https://datatracker.ietf.org/doc/html/rfc5322 (https://datatracker.ietf.org/doc/html/rfc5322#section-2.2.3) supports header folding so headers with more than 998 characters can be used in email. unf...
I am in the same boat. For a company project I'm required to apply folding to one of my headers, but this is currently not possible because of the limitation in the API.
By the looks of it there doesn't seem to be any progress regarding this either, unless I have missed something?