Daina Avizonis has learned to approach her inbox with a wariness normally characteristic of members of a bomb squad. The 41-year-old Redwood City, Calif., scientist scans the name of each sender, and if it is not someone she recognizes she zaps the message.

“I don’t open it at all,” she said.

To the dismay of mass marketers, many ordinary e-mail users take similar precautions, making it increasingly difficult for legitimate companies and nonprofits to conduct effective e-mail campaigns.

In response, AOL and Yahoo, two of the world’s largest e-mail providers, have said they will roll out an authentication service described as “certified e-mail” in the coming months.

The service, which will be provided to AOL and Yahoo by GoodmailSystems, will attach cryptographic “tokens” to e-mails belonging to senders whose legitimacy has been verified by GoodmailSystems employees.

Senders will pay between 1 cent and 1.25 cents for each certified message.

The tokens mark the message for delivery to the inbox and ensure they will not get trapped by a spam filter. In the inbox, they are tagged with a small graphic image that distinguishes them from regular mail.

Certified messages are scheduled to start showing up in the inboxes of the 26 million people who use AOL sometime in the next month or so. Yahoo said its service was not expected to start until later in the year and that it would be used primarily for e-mails involving some sort of financial transaction.

Richard Gingras, chief executive at Mountain View, Calif.-based GoodmailSystems, said a rigorous background check of senders would prevent spammers from becoming customers. Under the system, people still can independently decide that someone is a spammer and route their mail to a spam folder. However, they are encouraged to either unsubscribe from that mailing list or inform their e-mail provider or GoodmailSystems about any problem senders.

“For the consumer it’s great because it’s going to stand out as an e-mail that you instantly know is trustworthy, legitimate and authentic,” said Nicholas Graham, an AOL spokesman. “For commercial senders of e-mails, it’s a way to have your e-mail handled and delivered in a special way that stands out in the e-mail inbox.”