I see what you mean now - we'll probably drop that and/or combine this with remove-doubles.

sogo@gate:~$ /usr/sbin/sogo-tool check-doubles
The warning limit for folder records is set at 1000
sogo@gate:~$ echo $?
0

We need to have some information and not only a warning or at least nothing.
Why a limit is set to 1000, should not it be a parameter.
Even if i can ignored the warning, it will be nice to get some output show which entry it is checking.

The command is pretty fast if you look at the number of duplicated contacts i have in the DB.

The "check-doubles" was originally meant for addressbooks which were duplicated each time thunderbird was launched. That's why it's so basic and useless for you. What you can do is run remove-doubles directly, knowing that it will affect your DB. The command works quite well though and performs a score-based selections of cards to remove, so as to prefer most complete cards.