Outlook et thunderbird plugin are not available for odoo v8 or trunk version. But yes you can install them for the old version without any problem. Good work

I'm trying to join emails to opportunities, is there another way to do it with V8 ? mails feature do not give this possibility we can only check our emails.
 

Strange, because Odoo Online has this functionality (and in fact it is based on version 8)

it only works with dated versions of outlook though