The following maintenance can be done on any list to improve its quality for mailings as well as in-house administrative use:

Fix/add missing zip codes
Split combined fields (city/zip, names, etc.)
Add gender codes to names
Reformat records, put data into proper fields
Sort by any criteria
Search for and eliminate corrupt data (bad characters)
Search for and eliminate/combine duplicate records
Data quality analysis by fields or column positions

We have sophisticated matching software that can take any list and match it against any other list using name/address components and phone numbers. The resulting matches can be used for updating, enhancing/appending or suppression purposes.