For all its pitfalls and dangers, one of the great things about the Internet today is that it gives people a far wider range of experiences and choices. We can meet more people, learn more things, and even make more money than ever before. So, applying for a job online is something that will probably also increase as companies realize the convenience of recruiting online.
So, how to approach a company whose only contact option is email?
Well, it depends on some things.
The first thing to look for is if the job and its requirements are clear.
If you know what job you're applying for, you could approach this like a cover letter on a traditional CV. You could start with something like "Dear Sir or Madam" or "To Whom It May Concern." If you do not want to be that formal, you could start with a simple "Good Day." If a name is included, use it, as in "Dear Mr. Jay" or "Dear Ms. Ash."
Next, explain where you found the job listing, why you are a good candidate, and attach a resume. If no resume is requested, you might include a suggestion that you can provide a resume if necessary.
If no specific job is described, your job is to find out what the recruiter is looking for. Use one of the address methods mentioned above. Explain where you saw the ad, and then briefly ask the employer for guidelines to apply for the listed job.
In either case, the important thing is to be as brief as possible while also being as clear as possible, especially when you're offering details about yourself and your qualifications.
I hope these suggestions are helpful to you. Good luck!