regex double checking

I want to catch all mail sent through

        relay.bt.net
        relay2.bt.net
        majordomo.netcom.com
        listless.netcom.com
        mail5.netcom.com
        mail6.netcom.com
        mail2.netcom.com
        mail3.netcom.com        

I'm still new at regexes, but I think these are correct for catching the  
above hosts in procmail:

relay(2)?\.bt\.NET
        
(majordomo|listless|mail(2|3|5|6)?)\.netcom\.com

Are those right?

TjL