The server's positive reply to the end-of-data, as exemplified, implies that the server has taken the responsibility of delivering the message. A message can be doubled if there is a communication failure at this time, e.g. due to a power outage: Until the sender has received that 250 Ok reply, it must assume the message was not delivered. On the other hand, after the receiver has decided to accept the message, it must assume the message has been delivered to it. Thus, during this time span, both agents have active copies of the message that they will try to deliver. The probability that a communication failure occurs exactly at this step is directly proportional to the amount of filtering that the server performs on the message body, most often for anti-spam purposes. The limiting timeout is specified to be 10 minutes.
The server's positive reply to the end-of-data as exemplified implies that the server has taken the responsibility of delivering the message A message can be doubled if there is a communication failure at this time eg due to a power outage Until the sender has received that 250 Ok reply it must assume the message was not delivered On the other hand after the receiver has decided to accept the message it must assume the message has been delivered to it Thus during this time span both agents have active copies of the message that they will try to deliver The probability that a communication failure occurs exactly at this step is directly proportional to the amount of filtering that the server performs on the message body most often for anti-spam purposes The limiting timeout is specified to be 10 minutes