  * provide feature "builder" when needed crate is in Debian
    * mail-builder
  * provide feature "dkim" when needed crate is in Debian
    * mail-auth
  * provide feature "parser" when needed crate is in Debian
    * mail-parser
  * provide features "aws_lc_rs", "fips" "logging", "ring" and "tls12"
    when needed crate branches are in Debian
    * rustls v0.23
    * tokio-rustls v0.26
