Arriving at work recently, San Francisco police officer Nicole Jones was confronted with something unfamiliar: an email message.

The email was prosaic, containing a daily newsletter update from her station captain. But the email was unusual because it was the first one Ms. Jones received in her new San Francisco Police Department email account. "No one ever mentioned being able to have an email address from the time I started" two years ago because the department didn't give email accounts then, said the 27-year-old, who works...