Usually to be called by a scheduler, e.g. cron. If the provided day of
year matches those of the config the report is run as otherwise specified in
config. Functions called upon are expected to return a character string
providing a path to a file that can be attached to an email or, in case of a
bulletin, the email body itself. For bulletins, files cannot be attached.
The email itself is prepared and sent to recipients defined in the config