Declining a job offer by email is the next option, if you can't contact an interviewer by phone. The speed and convenience of email make it an ideal response method. Don't check professionalism at the door, however. Whether you take the job or not, what you say and how you say it still matters. In two or three paragraphs, you must clearly and succinctly state your decision without offending the hiring manager's sensibilities.
Advantages and Disadvantages
Consider email's pros and cons when crafting your message. A well-written email can impress an employer, while a poorly-worded or misspelled message will suggest a lack of professionalism. The ability to forward email also raises the risk of the wrong person reading your message, advises Converse College's guidelines for job seekers. Never write anything you don't want others to see. Once an email goes out, you can't take it back.
Watch Your Formatting
State your reason for writing in the subject line. For example, you could say, "Your Offer," so the interviewer knows that you're following up. Choose a font that's easy to read. Avoid using large fonts or all capital letters, which is the email equivalent of shouting or screaming. Make sure that your contact address is professional. Emails from "hotguy" or "sexygirl" will cause a hiring manager to doubt your professionalism and delete your message without reading it.
Be Concise and Businesslike
Respect the recipient's time. In your first paragraph's opening line, reference the interview date, but get right to your point. Express appreciation for the offer that you now decline. How much you reveal depends on your reason. For example, if a better offer or salary prompted your decision, say so, suggests Marjie Terry, a workplace communication consultant interviewed in Forbes magazine's August 2012 article, "How to Turn Down a Job Offer." If the position didn't seem like a good fit, then say, "After much thought, I've accepted an opportunity that's more in line with my current career goals."
Soften the Blow
Strike a warmer tone in your second paragraph to ease any potential fallout from your reply. Start off by saying, "I really enjoyed meeting you and the rest of your team." Add a sentence or two expressing how much you appreciated the opportunity, and give the hiring manager your best wishes . For example, you might say, "I only wish that circumstances would have allowed me to accept your offer. Thanks again for your interest, and best wishes for your future."
Other Rules to Remember
Re-read your response one last time before it goes out. Unlike face-to-face communication, email doesn't convey every nuance of a conversation -- so make sure that your message reflects what you're really trying to say. Keep copies of all emails that you send or receive, and don't automatically purge previous ones from your inbox. Otherwise, you may miss the final responses from the hiring manager.