Three other Horde applications, Imp 3.2.1 (WebMail), Turba 1.2 (AddressBook) and Nag 1.1 (TaskList) were intergrated in one single package named ImpXoopsMail, ImpXoopsMail has also been released recently.
All these modules require at least Horde Framework 2.3.1, a recent version of PEAR, PHP DOMXML and gettext extension.
(All merits should go to the Horde Dev. Team and all imperfections are mine, please DO NOT repport XingSLI and ImpXoopsMail errors in Horde Support Forums.)