Email address etiquette - Which address should I use to contact professors?
Personal email is OK, as long as it doesn't look too unserious (mickeymouse666@gmail.com is bad). Gmail looks more professional than other providers, but not by much.
Avoid email addresses that will expire soon. Unfortunately, many university addresses are like that. An expired address means you won't get late followup answers (and trust me, there are emails threads in research that span decades).
Avoid anything with alumni in it. Many people have a delete reflex when they see the word "alumnus", as it mostly appears in the context of panhandling by alumni orgs.
There is nothing pretentious about .edu addresses.