Official e-mail

How should I begin an official e-mail if I don't know who I am writing to? I mean, normally I would write "Dear x", but when I have to send an e-mail to an institution, what should I write?

When writing a formal email without knowing the name of the receiver, I would tend to fall back on standard letter writing style, especially for job applications and the like:

Dear Sir/Madam,

Or if the email doesn't need such an air of formality (for less important things), I'd write a simple:

Hello,

Or perhaps:

Hello [company name],

If you don't know a person's name or gender, avoid

"To whom it may concern."

Instead, use the job title or a generic greeting:

Dear Recruiter: Dear Claims Adjustor: Dear Sir or Madam: