Recall a message
From MozillaZine Knowledge Base
This article was written for Thunderbird but also applies to the Mozilla Suite.
For example, Microsoft Exchange servers support an Outlook user recalling a message. That only works if both the sender and recipient use Microsoft Exchange servers as thier mail servers, both mail servers are configured to work together and both the sender and recipient use Microsoft e-mail clients that support that functionality. That means you typically can only do this if both of you work for the same corporation. If the recipient uses a non-compatible e-mail client it never sees the recall request. If the recipient uses Outlook you still can't force a recall of the message if they've already read it. The details vary with other manufacturers' products, but it always requires both the sender and the recipient to use special software.
The "Undo Send" Gmail Labs add-on for Gmail appears to recall a message if you press it within thirty seconds of sending the message. However, it doesn't really recall the message, Gmail just holds it for thirty seconds before sending it in case you change your mind. The BlunderDelay [No longer maintained] add-on for Thunderbird does the same type of thing. It queues messages in the Outbox folder (Unsent Messages folder if you're using Thunderbird 2), to be sent at regular intervals. This gives you a chance to change your mind and delete or edit the message before its actually sent. Another workaround would be to install the Send Later extension and use the options in the compose window to schedule when you want to send the message.
There is a commercial service that you can configure like a SMTP server that lets you recall a message regardless of the recipient's mail server and e-mail client. Rather than sending the actual message to the recipient it converts the message to a web page on their server, and then sends a HTML mail message that contains a embedded link to a picture of the original message to the recipient. The subscriber could then log onto the company's web site and alter/delete the message whenever they want since it's still stored on the company's server. However, the recipient could still save the 'message' as a image file and view that after the message was recalled. The easiest way to detect one of these messages might be to default to viewing messages as plain text since you'd see the URL instead.