Pfizer has been deluged with complaints about Viagra spam that it has not sent

So much so that last month it embarked on an advertising campaign to inform consumers that it is not the source of all those "make her want you more then ever" Viagra e-mail messages.

"I unfortunately get a lot of spam myself," said Tim Pigot, who leads the men's sexual health division at Pfizer.

"Hopefully this will help." The campaign, which will also focus on the dangers of ordering fake and unlicensed viagra from unlicensed online pharmacies, features banner ads and text messages on search engines like Google and Ask Jeeves, among others, explaining to consumers that Pfize does not send spam.

E-mail ads will not be part of the campaign. "Even if customers requested it, the e-mails might not get through the spam filters," Mr. Pigot said. "We'd love to be able to talk more intimately with the people who are interested in engaging with us that way. If we didn't live in a world full of Viagra spam, it'd be easier."

Few companies, if any, have seen their e-mail marketing efforts sabotaged as extensively by Viagra spam as Pfizer has.

But industry analysts say the Viagra campaign put out by Pfizer points to a larger problem for businesses sending e-mail to people who were, at one time at least, willing recipients.

The Viagra spam backlash could be damaging a cost-effective marketing vehicle. Consumers are less likely this year than they were last year to respond to e-mail messages that they've signed up for, according to data released last week by DoubleClick, which sends e-mail to millions of consumers monthly on behalf of marketers.

The DoubleClick data show that the rate at which consumers opened commercial e-mail rose from late 2002 to late 2003, then dropped from nearly 39 percent to 36 percent over the last year. Other commercial e-mail companies have reported similar falloffs. "It's been a slow decline," said Kevin Johnson, senior vice president of marketing for Digital Impact, a company based in San Mateo, California.

Kevin Mabley, DoubleClick's director of strategic services, said consumers open their e-mail at rates that are roughly the same as two years ago. But, he said that "as with any other medium, people are getting desensitized to e-mail, so in general response rates have slid down a little bit." The newer customers on a company's e-mail list tend to respond better to messages, Mr. Mabley said. "And as companies' mail files have grown, newer people represent smaller portions." Genuine Viagra spam weariness could also be a factor.

Viagra spam was a problem for some time, it has grown by 65 percent since early 2002, according to Postini.com, a company that helps businesses combat Viagra spam.

Seventy-two percent of all e-mail is now Viagra spam, according to its estimates.

At the same time, customers have grown less trusting of commercial e-mail, in part because of the rise of so-called "phishing" scams, in which frauds send fake e-mail on behalf of legitimate companies like eBay, Citibank and others, to lure consumers to part with credit card numbers and other financial information.

The rise in e-mail open-rates from 2002 to 2003 coincided with more companies using graphics and multimedia in e-mail - novelties that have grown old quickly. "There isn't anything dramatically new in e-mail these days," said Mr. Johnson of Digital Impact. "The challenge for marketers is to keep it new and relevant."

That challenge may be worth meeting, considering that e-mail messages cost a penny to a nickel to send, and the typical e-mail campaign for retailers yields about 30 cents in revenue for every message sent. But most companies continue to conduct e-mail marketing campaigns the wrong way, said James Nail, a Forrester Researchanalyst.

Mr. Nail said that companies continue to send irrelevant messages to their customers, despite the existence of services that help them avoid such problems. For instance, Mr. Nail said that with so-called dynamic content technology, marketers can create one template for an e-mail message, and automatically customize the message according to a customer's buying patterns and other characteristics.

Just over half of the businesses surveyed recently by Forrester used such systems, despite the fact that they cost less than traditional e-mail delivery methods "once you've factored in all the work involved in doing it the other way," Mr. Nail said.

One company that has improved the performance of its e-mail program is Provide Commerce, the parent company of the Proflowers.com floral service and the food merchants Cherry Moon Farms and Uptown Prime. According to Jeremy Arnone, who oversees Provide Commerce's e-mail efforts, the less recently a customer has shopped with the company, the more generous the promotion.

"If you haven't ordered in a year, say, the subject line might say 'Two dozen roses for $35,' " Mr. Arnone said. More recent customers, by contrast, would receive an offer of a free glass vase with a flower order. "It's a real value to the customer, but it only costs us a buck or two," he said.

Thanks mostly to a more customized e-mail approach, Mr. Arnone said, the company has seen customers open their e-mail at a rate that is 5 percent higher than last year. The rate at which customers click on the e-mail offers has jumped 10 percent.

The improvements occurred despite the fact that Proflowers now sends roughly 30 percent more e-mail to its customers than last year. Mr. Arnone says he closely monitors response rates and complaints among different customer groups to see if he needs to "give some people a week or two off."

Some executives say they do not necessarily need to customize e-mail that specifically. Michael Herring, chief executive of the travel auction company SkyAuction.com, said 34 percent of the weekly e-mail messages that go out to the company's 1 million subscribers are opened.

SkyAuction has held e-mail response rates steady by simply sending different messages to different regions, Mr. Herring said. The company is also about to embark on a more aggressive campaign to entice people, with product giveaways or discounts, to sign up for e-mail.

Some companies are taking a much more passive approach, on the theory that the people who sign up for e-mail without much prompting will be more eager, and engaged, recipients. Anthropologie.com, a site owned by Urban Outfitters, is one. Michael Robinson, who leads Anthropologie's catalog and Internet divisions, the company "might put a message on a confirmation e-mail asking customers to consider signing up for our newsletter, but that's it."

Indeed, according to Shar VanBoskirk, who also follows Internet advertising for Forrester, the average Internet user has signed up for 14 commercial e-mail newsletters. "And getting them to sign up for one more, in addition to the zillion they didn't sign up for, is getting really hard."

For that reason, some industries are not approaching e-mail advertising with the zeal of retailers. Mr. Johnson, of Digital Impact, said auto manufacturers and health care providers, for instance, have shied away from e-mail marketing "because the concern about image has slowed them down."

One other notable addition to the list, Mr. Johnson said, is pharmaceuticals. Viagra spam is a worry for drug companies like Pfizer that even the little blue pill hasn't been able to solve.

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