Generally, students should feel free to email teachers questions or other information. 

Can I email my teacher any time?
Each teacher has their own expectations and needs when it comes to email communication. You may send an email at any time, but most teachers will stop checking and responding to email at some point in the afternoon or evening. You may ask your teacher if there are better times than others to send questions via email, though a teacher’s response via email on the same day is never guaranteed. Whenever possible, time-sensitive requests should be handled in person. This is particularly true with extensions. An extension should not be requested last-minute as this shows a lack of planning. Extensions should be requested substantially ahead of time, not the night before. Requesting an extension the night before shows a lack of planning, not a genuine need for an extension.

How often do I need to check my email?
Students are expected to check their email daily during the academic year.

Do I always need to respond to emails?
Students are expected to respond to all emails that are sent by their teachers specifically to them (e.g. “Dear Mortimer…” as opposed to “Dear class…”). When teachers do not receive a response, they do not know whether you have received and understood their message. Responding with a note like the following is an example of respectful and clear communication:
Hi Willow,
I got your email, and I understand that I need to submit the next part of the project by Thursday. Thanks so much.
Best,
Elora Danan

Can I submit homework assignments via email?
Please do not submit homework assignments through email unless specifically requested by the teacher.

What language and tone should I use when emailing with teachers?
When communicating by email, students should use a formal style and not allow their writing to decay into abbreviations, sentence fragments, emoticons, and other contemporary habits for electronic communications. Emails should have proper spelling, punctuation, capitalization, and grammar. Notes should have opening greetings (“Dear Reginald,”) and closings (“Your Grateful Student, Priscilla”). If you want your reader to understand your letter, be able to focus on its point, and respond effectively, please take the time to respect these guidelines. Here is an example:
Hi Spike Lee,
I hope you’re well. I was just wondering, is it okay if I read ahead in the book tonight?
Thanks,
Radio Raheem