supressing log messages

[tmc-au]

Is there a way to suppress log messages such that all I get in auth.log are fail and success events?

Specifically I would like to get rid of theses:

Oct 9 17:41:03 celaeno saslauthd[53501]: pam_mysql - SELECT returned no result.
Oct 9 17:41:03 celaeno saslauthd[53501]: pam_mysql - SELECT returned no result.
Oct 9 17:41:03 celaeno saslauthd[53501]: DEBUG: auth_pam: pam_authenticate failed: User not known to the underlying authentication module

but keep these:

Oct 9 17:41:03 celaeno saslauthd[53501]: : auth failure: [user=lia.b] [service=smtp] [realm=] [mech=pam] [reason=PAM auth error]

[NigelCunningham]

I'll see what I can do. Apologies for the delay in replying.