Trigve Siver: > Thanks for reply. > > Could some post the except from standard where this is defined to be able to > argue with relayhost provider, please?
RFC 5321 is the current SMTP definition. 6.1. Reliable Delivery and Replies by Email ... If there is a delivery failure after acceptance of a message, the receiver-SMTP MUST formulate and mail a notification message. This notification MUST be sent using a null ("<>") reverse-path in the envelope. The recipient of this notification MUST be the address from the envelope return path (or the Return-Path: line). However, if this address is null ("<>"), the receiver-SMTP MUST NOT send a notification.