List Metadata fields used in messages.
metadata_options()
A vector
containing message metadata fields.
This function lists message metadata used by IMAP servers, according to the RFC 2060 (Crispin, 1996).
Crispin, M., "Internet Message Access Protocol - Version 4rev1", RFC 2060, doi:10.17487/RFC2060 , December 1996, https://www.rfc-editor.org/info/rfc2060.
if (FALSE) { library(mRpostman) metadata_options() }