Mail.log full of "no SASL support" messages

There are a lot of these warnings in mail.log. Can anyone tell me what exactly causes them and how to fix it? When looking at the Google results, I thinks it’s a more complicated problem. Here’s some complete example, maybe it helps:

Jun 24 08:06:57 box postfix/smtpd[26814]: connect from mout.gmx.net[212.227.15.19]
Jun 24 08:06:57 box postfix/smtpd[26814]: warning: restriction `reject_authenticated_sender_login_mismatch' ignored: no SASL support
Jun 24 08:06:57 box postgrey[642]: action=pass, reason=triplet found, client_name=mout.gmx.net, client_address=212.227.15.19/32, sender=someone@gmx.de, recipient=me@box.miab
Jun 24 08:06:57 box postfix/smtpd[26814]: 89FEA64007A: client=mout.gmx.net[212.227.15.19]
Jun 24 08:06:57 box postfix/cleanup[26817]: 89FEA64007A: message-id=<INX.someid.bounce12@inx1and1.de>
Jun 24 08:06:57 box opendkim[23131]: 89FEA64007A: s=isystem1 d=fmp.gmxnet.de SSL
Jun 24 08:06:57 box opendmarc[572]: implicit authentication service: me@box.miab
Jun 24 08:06:57 box opendmarc[572]: 89FEA64007A ignoring Authentication-Results at 20 from mqgmx024.server.lan
Jun 24 08:06:57 box opendmarc[572]: 89FEA64007A: fmp.gmxnet.de none
Jun 24 08:06:57 box postfix/qmgr[32617]: 89FEA64007A: from=<someone@gmx.de>, size=34214, nrcpt=1 (queue active)
Jun 24 08:06:57 box postfix/smtpd[26814]: disconnect from mout.gmx.net[212.227.15.19] ehlo=2 starttls=1 mail=1 rcpt=1 data=1 quit=1 commands=7
Jun 24 08:06:57 box spampd[21716]: processing message <INX.someid.bounce12@inx1and1.de> for <me@box.miab>
Jun 24 08:07:00 box spampd[21716]: clean message <INX.someid.bounce12@inx1and1.de> (0.01/5.00) from <someone@gmx.de> for <me@box.miab> in 2.80s, 34438 bytes.
Jun 24 08:07:00 box postfix/lmtp[26818]: 89FEA64007A: to=<me@box.miab>, relay=127.0.0.1[127.0.0.1]:10025, delay=3.3, delays=0.41/0/0.01/2.9, dsn=2.0.0, status=sent (250 2.0.0 <me@box.miab> oDATMIFoEF3DaAAAr2IX0w Saved)
Jun 24 08:07:00 box postfix/qmgr[32617]: 89FEA64007A: removed

In this case it was a reputable, huge mailprovider. But the warning happens with all kind of other senders, too.

PS: Sorry about the title, wouldn’t let me use a better one.