simply updating the mail send out when acknowledging a newly reported
bug to additionally mention that one has to subscribe to receive any
updates would help a lot already, I think. Currently that mail only
mentions "If you wish to submit further information on this problem,
please send it to firstname.lastname@example.org". An additional sentence like "If
you wish to receive information about further updates on this problem,
please subscribe to email@example.com." would do the job, IMHO.