Professors/faculty receive many emails asking for internships, PhD student positions, etc. I even receive such requests as a postdoc -- I am not even able to offer such positions!
Almost all of these emails are low-quality. Namely, they are not specific to the professor's research and have the appearance of being mass emails sent to hundreds of recipients without much thought. Replying to them is a waste of time.
As a result, professors are accustomed to ignoring such emails. It is quite possible that your email was treated as spam.
Here are a few suggestions to avoid your email being ignored:
- Ensure that your email is relevant to the recipient. If you are asking them to be your PhD supervisor, explain why. What about their research interests you? (At the very very least, get their name right!)
- Have a professor you know introduce you. The email will be more credible if it comes from someone the recipient has heard of. In essence, this serves as a recommendation.
- Make sure your email includes enough information about you. Briefly introduce yourself (i.e. your qualifications) and you could even attach a CV or link to a website with more information about yourself.
- Get to the point. Academics get so much email they may not read past the subject line before ignoring your email. Keep it short and make sure the subject and first sentence/paragraph of your email are clear, concise, and to the point. If you have a sponsor already, don't leave that until halfway through your long email.