what is this: auxpropfunc error no mechanism available?

Today, when I launched the Console on my XServe I found the "console.log" completely full with the following (just a small snippet):

Jun 19 09:46:42 pkmainserver postfix/smtpd\[13032\]: auxpropfunc error no mechanism available\n
Jun 19 09:46:43 pkmainserver postfix/smtpd\[13037\]: auxpropfunc error no mechanism available\n
Jun 19 09:47:19 pkmainserver postfix/smtpd\[13045\]: auxpropfunc error no mechanism available\n
Jun 19 09:49:22 pkmainserver postfix/smtpd\[13060\]: auxpropfunc error no mechanism available\n
Jun 19 09:51:28 pkmainserver postfix/smtpd\[13083\]: auxpropfunc error no mechanism available\n
Jun 19 09:52:12 pkmainserver postfix/smtpd\[13091\]: auxpropfunc error no mechanism available\n
Jun 19 09:55:00 pkmainserver postfix/smtpd\[13108\]: auxpropfunc error no mechanism available\n
Jun 19 09:59:15 pkmainserver postfix/smtpd\[13126\]: auxpropfunc error no mechanism available\n
Jun 19 09:59:16 pkmainserver postfix/smtpd\[13132\]: auxpropfunc error no mechanism available\n
Jun 19 10:04:13 pkmainserver postfix/smtpd\[13164\]: auxpropfunc error no mechanism available\n
Jun 19 10:04:16 pkmainserver postfix/smtpd\[13174\]: auxpropfunc error no mechanism available\n
Jun 19 10:10:48 pkmainserver postfix/smtpd\[13210\]: auxpropfunc error no mechanism available\n
Jun 19 10:10:49 pkmainserver postfix/smtpd\[13215\]: auxpropfunc error no mechanism available\n
Jun 19 10:16:36 pkmainserver postfix/smtpd\[13246\]: auxpropfunc error no mechanism available\n
Jun 19 10:16:37 pkmainserver postfix/smtpd\[13251\]: auxpropfunc error no mechanism available\n
Jun 19 10:18:59 pkmainserver postfix/smtpd\[13261\]: auxpropfunc error no mechanism available\n
Jun 19 10:19:29 pkmainserver postfix/smtpd\[13269\]: auxpropfunc error no mechanism available\n

I have no ideia as of what might be causing this. The mail service is working as it should and apparently no problems with that.
Any help is greatly appreciated!
Thank you.