sympl-mail: Review Exim configuration
The Exim configuration has been inherited from older versions of Symbiosis, and has diverged a fair bit from the default Debian configuration. It's worth a full review of the config to bring it more in line and avoid issues later on.
One specific mention was that we should
Comment out the rfc_1413 lines in 00-main/60-general-options and add a separate file with an ‘official’ exim4 recipe for turning ident off.
...which seems like a good start.