Okay. as the message-ids and the bounce addresses are different, this definitely looks like an OpenACS Problem. Will dig into this later.
==============
Apr 22 09:03:55 ipx10216 postfix/cleanup[24250]: 137752703B9: message-id= mailto:-1681110056.1145689435.oacs@www.sussdorff.de>
Apr 22 09:03:55 ipx10216 postfix/qmgr[1052]: 137752703B9: from=bounce-446-BB768B9094CC4BD4B19AD87C09A109263981E3FF-@www.sussdorff.de>, size=1268, nrcpt=1 (queue active)
Apr 22 09:03:55 ipx10216 postfix/smtp[24251]: 137752703B9: to= mailto:sussdorff@sussdorff.de>, relay=in1.smtp.messagingengine.com[66.111.4.73], delay=0, status=sent (250 Ok: queued as 8CAEF2D10)
Apr 22 09:04:55 ipx10216 postfix/pickup[24176]: 137612703B9: uid=501 from= mailto:bounce-446-1B913602AF0DF977F44848FD9F9094B443ACFC58-@www.sussdorff.de>
Apr 22 09:04:55 ipx10216 postfix/cleanup[24250]: 137612703B9: message-id= mailto:-1621110986.1145689495.oacs@www.sussdorff.de>
Apr 22 09:04:55 ipx10216 postfix/qmgr[1052]: 137612703B9: from=bounce-446-1B913602AF0DF977F44848FD9F9094B443ACFC58-@www.sussdorff.de>, size=1268, nrcpt=1 (queue active)
Apr 22 09:04:56 ipx10216 postfix/smtp[24251]: 137612703B9: to= mailto:sussdorff@sussdorff.de>, relay=in1.smtp.messagingengine.com[66.111.4.72], delay=1, status=sent (250 Ok: queued as 28462ADBC)