Recalling an email means attempting to retrieve or delete a message you have already sent before the recipient reads it. This feature allows you to either delete the unread email or replace it with a corrected version. The recall is most effective when both sender and recipient are using the same email system, such as Microsoft Outlook within the same organization, and the email has not been opened by the recipient yet. If the recipient has already read the email or is using a different email service, the recall will generally fail. Even if successful, the recipient may sometimes see a notification about the recall attempt.

For example, Microsoft Outlook has a "Recall This Message" function that allows the sender to attempt to remove the email from the recipient's inbox or replace it, provided certain conditions are met (same email system, unread email). Gmail also has a short "Undo Send" window after sending an email, during which the user can cancel sending, effectively recalling the email immediately after sending.

In summary, recalling an email means retracting a sent message under specific conditions to prevent the recipient from reading it.