E-Mail Protocol

Is there an email protocol you follow? Is there an unwritten law that says you must answer an email within a certain time frame? I ask this in lieu of a few emails i am waiting to recieve from work colleauges. It's an ongoing "thing" with all my colleauges here in town, they take up to a month to answer me! I could phone them and ask the questions but i am in front of the computer so i email them. Many a meeting has been missed by some because they have not checked their emails! One or two have even screwed up their court dates because they've not checked emails. Now, i'm thinking this may be an age thing. I am the youngest person in the firm i work for, everyone else is old enough to be my mother or father so your looking 55+, i wonder if its a technology thing.....so used to using a phone, not used to using a computer! Blah! these are all professional people, course they know how to use a computer! I have an unwritten rule, i answer work emails ASAP, i answer personal emails within 36hrs. So why the hell can't anyone else do that?
till next time, Michelle.