garbled mail exchange

   ----- Transcript of session follows -----                                    
...while talking to mx0.gmx.net.:                                              
>>>RCPT To:<xxx.xxx@gmx.at>                                             
<<<550-5.7.1 {mx099} The IP address of the server you are using to connect to GMX is listed in
<<<550-5.7.1 the XBL Blocking List (CBL + NJABL).
<<<550-5.7.1 For additional information, please visit
<<<550-5.7.1 http://www.spamhaus.org/query/bl?ip=217.196.64.204 and
<<<550 5.7.1 ( http://portal.gmx.net/serverrules )
5505.1.1 <xxx.xxx@gmx.at>... User unknown

Hilarious, but no problem - I have a clean unix network and no trojans, no obvious proxies on the mail server, so this must be a glitch. CBL has a very straightforward no questions asked unlisting policy, half an hour later I'm clean as a sheet and try to resend - same result.

Next day:

   ----- Transcript of session follows -----                                    
... while talking to mx0.gmx.net.:
>>> RCPT To:<xxx.xxx@gmx.at>
<<< 550-5.7.1 {mx027} Sorry, your helo has been denied.
<<< 550 5.7.1 ( http://portal.gmx.net/serverrules )
550 5.1.1 <xxx.xxx@gmx.at>... User unknown

Solution: my HELO indeed contained weird stuff, it seems dialup.m4 was broken. doh.