Adjusting TTL for PTR records

We're using Microsoft DNS on Microsoft Server 2003. Our mail server seems to be listed on the SORBS blackhole list, since the TTL for our PTR record is less than 43200. How can I change this so we can get delisted?
 
Thank you.

Thanks for information!!!
I was really searching this type of information in last few days.
This information will give me lot of help in near future.
Thanks a lot




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silver bangles