Start a polite e-mail

Hello,

I suppose this question is asked before but i can't find it in the threads. I want to write an e-mail to a firm to ask some information. It's a general e-mail address, so I don't know the name nor sex of the man/woman who will receive my mail. How do I start the letter in a polite way. I suppose it's not appropriate to start with: hi or hello.. what is your opinion?

Thank you very much!

Ilse
A Belgian med student