Email address etiquette - Which address should I use to contact professors? I am currently a master's student outside the U.S., and I plan to contact professors in U.S. universities for PhD applications. I have a bunch of email addresses available, and I don't know which one is the most appropriate for communication.

My main objective is to make sure my email doesn't get lost in the spam folder, and a decent first impression would not hurt.

My options:

(1) surname@university.edu.xx: Email given from the current institution where I attend.

(2) surname@alumni.university.edu.xx: Alumni email from the university where I got my undergrad degree.

(3) f.surname@university.edu: Email from a well known U.S. university where I spent a year as an exchange student.

(4) firstname.surname@gmail.com : Private email address

My question is, do you think the possibility of getting a response depends on the email domain? What email domain should I use?

A friend of mine who ended up at a top-5 grad program suggested me to use (3), saying that it could increase my chances of getting a response. However I am cautious that it may look pretentious or delusional, considering I had been there some time ago. 

Am I overthinking this?
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.