The sendmail program initializes maps in passes so that it can open a map for reading or rebuild. That is, pass 0 opens it for reading only, and passes 1 and 2 open it for updating. This gives sendmail the opportunity to detect optional maps. The -d38.3 debugging switch causes sendmail to print wrong pass every time it skips rebuilding because the pass is inappropriate:

map_init(dbtype:name, file , pass)   from -d38.2
wrong pass

The -d38.3 debugging switch also causes sendmail to print a failure message if an implicit database type does not exist:

impl_map_open(name, file, mode)    from -d38.2
no map file