With many job postings now requiring candidates to apply via email, first impressions are made not with a handshake but with words on a computer screen. How formal should your first email to a recruiter be?

Just as it's usually a good idea to dress your best for an interview, emails also should be professional and polished, say hiring managers. If you decide capital letters aren't worth your time, you might be in for a long job search.

Kristen O'Hara, a senior recruiter for Dallas-based Affiliated Computer Services Inc., an information-technology outsourcing company, says she has seen it all, including emails with funky fonts and distracting backgrounds.

"Honestly, there are some emails that have completely ruined a candidate's chances for me," she says.

To avoid sabotaging your job search, here are some tips to follow when sending cover letters by email:

Job recruiters report that young professionals are the applicants most likely to send too-casual emails.

Liz Shupe, interim director of the career-development center at the University of Richmond, offers one explanation: "They're treating it like an IM."

When using Instant Messenger with friends and acquaintances, it's acceptable to use abbreviations and incomplete sentences and to forgo capital letters and punctuation. In business correspondence, however, stick to the rules your English teacher taught you.

"We tell our students that an email is the same exact thing as a cover letter, without the addresses on top," says Ms. Shupe.

Your adorable email background of puppies snuggling with kittens has got to go.

"I remember a particular email written in that 'comic' font," says Ms. O'Hara. "That's just not professional to be sending to a work contact." She recommends plain-vanilla fonts, such as Times New Roman and Arial, and black text on a white background.

Ms. O'Hara also warns against sending emails from quirky email addresses. Slackerboy@ or Sexgoddess@ might not get the chuckle you hope for. If you leave your cellphone number as a contact number, make sure your voicemail message is appropriate, and that means it shouldn't include music, she says.

Wynne Billings, a corporate recruiter, says many of the emails she reads show a lack of effort on the part of the applicant.

"It's like they just cut and paste the same cover letter to everything they're doing," says Ms. Billings, who works for Apex Systems Inc., a technology-staffing firm based in Glen Allen, Va. "It's so not catered toward our job."

It's a big plus if applicants can show they know a lot about the position they're applying for, Ms. Billings says. She recommends job hunters use part of the job description they feel matches their skills or experience to explain why they'd be good for the position. "Nine out of 10 people don't do that," she says.

"Get to the point," says Hank Stringer, a former high-tech company recruiter in Austin, Texas.  He doesn't like it when candidates use gimmicks to try to attract attention, citing as an example a missive from one applicant that blathered on about high gas prices. Messages should be straightforward and concise, he says.  

Mr. Stringer, who founded Hire.com, a recruitment-management software and services firm, says recruiters often have only seconds to devote to each cover letter they receive, and many are looking for just three things: the titles of the positions you've held, the companies you've worked for and your educational background. Anything else, such as a long story about yourself, can get in the way, he says.

5. If attaching a cover letter, write a brief note in your email.

There's no rule about whether a formal cover letter should be attached to an email or whether the email itself can serve as a cover letter.

If you attach your cover letter, the text of your email can say: "I really want to work for your company, please see attached resume and cover letter," says Ms. Billings. "Even maybe just tell me briefly why you want to work for my company, just give me a sentence, then I'm going to open that cover letter and resume."

Mr. Stringer also warns against being too creative in the subject line of an email. He recommends: "Experienced candidate seeking position as [name of position]" or "Experienced candidate seeking position with [name of company]."

"Use one word to describe yourself, but do not go overboard," he says.