currently, the script is hardcoded for emails older than 1 day
this is a script because it is a simple operation and probably will be
called by a cronjob
there is no current need to have a separate table for keeping track of
the inboxes, since all emails are getting stored upon arrival and anyone
can access all mails from any rcpt address.
also, added a arrived_at column, as a utc unix timestamp. This serves
the obvious reason to have a ts on an email, but also allows this
service to delete old mail.
