Exchange Server 2007 (almost) EOL!
Just a quick reminder that Exchange Server 2007 will have no support after April 11th 2017. Although every install will continue without any issue after this date, it is a risk continuing the use of this product. Security fixes won't come available, but also little things like timezone/daylight savings changes aren't updated which could have a high impact in your organisation.
You can transition to Exchange Server 2010 but preferably Exchange Server 2013. However, I would suggest migrating to Exchange Server 2016 but as there is no coexistence you would have to do a double migration (via Exchange Server 2013) or migrate towards Office 365/Exchange Online. MVP Steve Goodman has written a nice blog post with all your options in more detail.