Are you sure you have the latests version of all the packages?
(Show us the output of "apt-cache policy ebox" and "apt-cache policy ebox-mail")
Anyway, if you first installed 1.3.10 and then updated, probably you have to reinstall the ebox-mail package due to a bug that was fixed later. To do this:
apt-get remove --purge ebox-mail
apt-get install ebox-mail
Hope this helps.