  * 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", "aws-lc-rs", "fips"
    when crates rustls and tokio-rustls provides needed features in Debian
    * aws_lc_rs
    * fips
