An autoreply problem can occur when the MTA receives a message that has been automatically forwarded from another system in some other administrative domain. For example, if a customer has a home account with sesta.com and the customer sets that account to automatically forward messages to their work account at siroe.com and if siroe.com uses Messaging Server and that user has set his account to autoreply a vacation message, then Messaging Server will have a problem sending out a vacation message.
The problem occurs because the sesta.com mail server changes the envelope To: address from firstname.lastname@example.org to email@example.com, but it will not change the To: header, which remains firstname.lastname@example.org. When the MTA receives the message, it looks at the header address only. It attempts to match this address with an address in the LDAP user directory. If it finds a match with someone who has set autoreply, then a vacation message is sent. Because there is no LDAP address match to email@example.com, no vacation message is sent. The problem is that the actual address is in the envelope and not in the header.
Since the recipient's address known to the remote system doing automatic forwarding isn't known to correspond to the user by the local system, there needs to be a way for the recipient to make such addresses known to the local system so vacation replies will be sent when necessary.
The :addresses argument to the Sieve vacation action provides this capability. It accepts a list of addresses that correspond to the recipient for purposes of making this check. The attribute defined by the MTA option LDAP_AUTOREPLY_ADDRESSES allows specification of such addresses in the user's LDAP entry.
To provide autoreply capability for messages that have been automatically forwarded from mail servers in some other administrative domain, the user or administrator would set the email addresses from where those messages may be forwarded to the attribute defined by LDAP_AUTOREPLY_ADDRESSES.