dirmngr is a server for managing and downloading OpenPGP and X.509 certificates, as well as updates and status signals related to those certificates. For OpenPGP, this means pulling from the public HKP/HKPS keyservers, or from LDAP servers. For X.509 this includes Certificate Revocation Lists (CRLs) and Online Certificate Status Protocol updates (OCSP). It is capable of using tor for network access.
MongoDB doesn't have official packages for Debian Stretch at this moment, so we'd have to install from the Jessie repository which will throw an error saying the dependency `libssl1.0.0` will not be satisfied.