Poor reputation is earned by the behaviour of the users of the MTA - if there is a genuine spammer, or the address is a new one and there is a huge flood of email coming from it (php bulletin board digests to tens of thousands of subscribers for example) the Internet community that feeds into the reputation engines flags this up and the reputation can be downgraded.
This may or may not be what is causing the "bounce back from Telecom" described. Without information about the sending MTA from the headers, no-one can check to see if there are any reputation issues.
One URL to check if a particular IP address, URI or domain has a poor reputation is:
Hope this helps.