Email Marketing can be an effective tool for recruiting when used correctly.   The number one rule is to only send mailings to people that opt-in to your list.   This means if you are recruiting job seekers then you should only send mailings to prospective applicants who choose to be contacted by employers.   If you are recruiting students for a college then you will want to only send mailings to students that provided their email address to a representative for future contact.  You delegitimize your institution by sending unsolicited emails which hurts your recruitment and can be damaging to your credibility.
The real advantage to using email marketing lies in sending cost- effective, targeted mailings.   Targeting your mailings to specific demographics is especially important when using email marketing for recruiting.  Your subscription forms for prospective recruits should include subscriber fields so that you can filter your mailing and send targeted newsletters to your subscribers.     A subscription form targeting a job seeker may include all or some of the following:  career field or industry, level of experience, zip code, and education.  A form that you would use for recruiting college students may include some or all of the following: GPA, major, school, college level, and zip code.   There may very well be overlap here especially for career oriented educational institutions that attract a number of adults looking to switch industries or receive job related training.
A word of caution when using email marketing for recruiting younger college bound students as they tend to be tech savvy and can be more resistant to marketing speak and tend to be less impressionable to traditional forms of advertising.   Email Marketing should not be used as a replacement for regular snail mail.   Rather, it should be presented as an alternate method of providing information to prospective applicants.   A recent national survey of high school juniors found that 64% of respondents preferred to receive college information through the mail rather than email.  College bound students these days are much more interactive and less respondent to static forms of marketing communication and language.  They respond more favorably to interactive forms of communication such as instant messaging, blogs, podcasts, personal emails, and text messaging.   If you do use email marketing then take advantage of personalization tags and sending filters so that your mailings are targeted to the demographic that you are reaching.
A trap that many recruitment companies and job boards using email marketing fall into is that they try to cram too much information or irrelevant content about different jobs in order to alert a reader’s attention.    This will confuse and annoy your readers and your mailing will be treated as junk mail.   Subscribers want to know how your email will benefit them so you should make the focus of your mailing clear and easy to understand.  Focus on a single job, recruiting company or package and the design of your newsletter should follow the company image you are using to present the job or job board to the job seeker.   This is again a good reason to ensure that your signup forms include lots of fields, provided they do not overwhelm the job seeker, so that you can use sending filters to send out targeted mailings.
You can also increase your response rate by improving your email design and email copywriting techniques.