i dont think you can use wildcards like that, you'll have to stick with @mail.ru @bk.ru heres a whole list from a email filter i use.
Code:
@mail.ru @bk.ru @list.ru @amorki.pl @acotraviag.com @bumz-vallera.com @mysoftware.ru @meta.ua @seznam.cz @mymail-in.net @fromru.com @mymail-in.net @buy-viagra-for-love.info @yandex.ru alextop@email.org @buy-discount-phentermine.info dabbdoo@tesco.net noreply@intwayz.net dizzypetrov@email.com @e-mail.net @e-mail.com zimmer@maxifeed.info @inbox.ru @lkjdfghu3.cn velesgoogle@email.net @tsenekov.ru @the-s-box-land.com ErikRose78@yahoo.co.uk nba11nba@gmail.com @mymail.com annetivanov@e-mail.com janechvs@gmail.org mutisita@gmail.com annettex@mymail.com alextex@gmail.com nba10nba@gmail.com annachvs@xmail.com maximtts@gmail.net janefrance@gmail.net
johnlittle@mymail.com adamdark@email.net
robrojus@inetum-editor.com @bonbon.net
alextex@gmail.com olgamarley@gmail.com velesusa@hotmail.com @ukr.net @xmail.com gregorshulz@gmail.com @ktsc.ru @e0theresa.info wusopiox@gmail.com @wp.pl bobjnr@gmail.com angeltop@hotmail.com cris.henry@yahoo.com @ua.fm dizzypitt@xmail.net milesmarley@gmail.com @gawab.com maximpetrov@xmail.org bobshulz@mymail.net henrycris@yahoo.com roberttop@hotmail.com @inmail24.com @ddeyeas.com dizzyswift@mymail.org alexusa@gmail.org ahmadenagad@gmail.com adampetrov@hotmail.com @rambler.ru @lenswet.ru @hotasd.com
@open.by @.by @searchroad.net @100-free-ringtone.info dftone.com @gmx.com @clickhunters.net @lvovs.com @punkass.com @wittystuff.info @webpopular.ru @lohjn.info @allfarm.cn @porno-haus.com @student.su @goolook.ru annetgoogle@xmail.org @jonnson.info bradgoogle@hotmail.com @mytop-in.net @bluebottle.com wete_baseball@email.it
Also try implementing stronger spam prevention measures, they shouldn't be able to even make it into the system really