[Koha] koha mail

Dear community, Our Fundamental library mail server and koha located on different servers. Such mail server we use sendmail program on linux ubuntu 12.04 and (we have mail account kohaflib@flib.sci.am) We use Koha 3.12.05 Tarball on Ubuntu 12.04. We want to use our mail server for sending notices to Koha patrons . How can we configure Koha to send email? Best regards, Araik