The envelope information is an envelope sender address followed by a list of envelope recipient addresses. The sender address is preceded by the letter F and terminated by a 0 byte. Each recipient address is preceded by the letter T and terminated by a 0 byte. The list of recipient addresses is terminated by an extra 0 byte. If qmail-queue sees end-of-file before the extra 0 byte, it aborts without placing the message into the queue.
Every envelope recipient address must contain a username, an @ sign, and a fully qualified domain name.
qmail-queue always adds a Received line to the top of the message. Other than this, qmail-queue does not inspect the message and does not enforce any restrictions on its contents. However, the recipients probably expect to see a proper header, as described in qmail-header(5) .