The -d38.12 debugging switch shows values being stored in maps that support updates:

db_map_store(name, key, value) 
ndbm_map_store(name, key, value) 
seq_map_store(name, key, value) 

Here, the name is either the name you gave to the database map with the K configuration command, or a name assigned internally by sendmail (such as aliases.files). The key is the key for the new value that is being stored, and the value is the value being assigned to that key.