kryptos
The conservative settings in the wiki are safe, and you should receive all legitimate email ie
config setprop qpsmtpd RBLList zen.spamhaus.org:whois.rfc-ignorant.org:dnsbl.njabl.org
signal-event email-update
The db settings in a stock sme7.2 which are disabled by default, do include some aggressive lists, and it is highly likely you will block some legitimate email, especially mail coming from popular free systems eg yahoo, hotmail, gmail, aol etc.
Refer to this old howto for some tips, most of which is still current, a couple/few of the lists are defunct now
http://wiki.contribs.org/Spam_blocking_tutorialAs you are aware there are quite a few additional lists shown in the Email wiki page.
http://wiki.contribs.org/Updating_to_SME_7.2#RHSBL_Servers