America Online has caused consternation among US not-for-profit and community groups over its plans for a 'two tier' email service.

Up to 500 not-for-profit organizations have sent an open letter to AOL protesting over the launch of its certified email service, where senders can opt to pay to guarantee delivery.

Charities fear their online communications could be blocked as spam if they do not pay for the service, being offered through third party provider Goodmail.

But AOL insists the service is an optional way for large senders to deliver authenticated legitimate email to users that have opted to receive it, and is a further weapon in the war against spammers.

In an attempt to conciliate not-for-profit protesters, the internet giant has promised a 'pro bono' service that will allow them to send certified email for free using a third-party provider.

The offer, however, cuts little ice. Comments Noah Winer of political advocacy group "They . . . haven't been clear on what the programme is so there is a little confusion about what they are offering."

He adds: "They make it sound the same as Goodmail but it's a separate tier, it wouldn't come into the inbox the same way. Goodmail users are the only ones that get guaranteed delivery, everybody else gets to run the gauntlet of spam filters."

Data sourced from Financial Times Online; additional content by WARC staff