First and foremost, you should always follow the directions on the posting. If the listing says “email resumes to firstname.lastname@example.org,” you should do just that. Send a short cover email and attach only your resume. Remember, this is an exercise in following directions, and that’s just as important as your qualifications. If a posting asks you to email both a resume and cover letter, you should attach your resume and formal cover letter, and you’ll also want to include a brief cover email, just in case no one reads the cover letter (a likely situation). “Attached please find my resume and cover letter for your consideration for the assistant position” is not sufficient. Write the CliffsNotes version of your cover letter in the email to help frame your application.
So how is a cover email different from a cover letter? The short answer: It’s about half as long. A cover letter will ideally be no longer than half a page—three short paragraphs: intro, relevant experience, and summary. A cover email will only be one paragraph—probably about four sentences. If a hiring manager isn’t asking for a cover letter, it’s because they don’t want to spend the time reading one. But it is good to express your intentions, especially if it’s not completely obvious from your resume why you’re applying for the job. So in a cover email, you should name the position you’re applying for, describe who you are, and state why you should be considered for this role. You’ll attach your resume, ask for an interview, thank the person you’re writing to for their time, and that’s it, you’re done. Make sure you keep it brief — hiring managers love candidates that can get their point across in a concise manner.
One final tip: Your cover email should be even more conversational than a cover letter. DO NOT copy and paste cover emails for multiple applications. It’s pretty obvious when you do this in a cover letter, but it’s impossible to ignore in a cover email. Open a fresh email for every application, and start from scratch — you’ll sound less like a robot and are a lot more likely to get a call.