By default, activeCollab uses MySQL FULLTEXT index for search. Even if it works great in most of the cases, sometimes MySQL can be configured not to index words shorter than 4 characters.

To correct this and configure MySQL to index 3-letter words (it is not recommended to go with shorter than 3 characters), you will need to set the value of ft_min_word_len directive in your my.cnf. Here is how:

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[mysqld]
ft_min_word_len=3

After you are done, you should restart your MySQL server and rebuild search indexes using the Administration > Indexes tool.