Forwarding to remote users in the same domain

This topic discusses the solution to the following problem.

Company A has 3 POP3 mailboxes at their ISP. Two of the POP3 mailboxes are for specific users while the third is for all the other addresses in the domain. Thus the 3 mailboxes are called

user1@a.com
user2@a.com
anyone@a.com

Company A wants to have all mail for user1 and user2 delivered from their FTGate to the Internet so that their ISP can place the mail is the user1 or user2 mailbox. So they go to the options for domain a.com and set the undeliverable mail option to forward the mail to the internet (Domain List/a.com/undeliverable). They then configure SmartPop to collect mail from the anyone@a.com mailbox and deliver to the appropriate mailboxes.

Problem

An outside user sends a message to noone@a.com and there is no mailbox for that address. SmartPop collect the message and delivers it to the domain, the domain sees it as being to an unknown address and sends it back to the internet which puts it back in the anyone@a.com mailbox thus causing a loop. This has two consequences, the message will go round in a loop until the ISP stops it, and if the mail were important but mis-addresses it would be lost.

Solution

The cause of the problem is that the domain is passing responsibility for the validity of the addresses to the ISP which does not have any way to know the validity of the addresses. The solution is for the administrator of FTGate to take responsibility and set the domain handling to either reject badly addressed mail or deliver it to a nominated local mailbox (Domain List/a.com/undeliverable)..

However, that leaves the problem of local users being able to email user1@a.com and user2@domain.com, there is no local mailbox in the domain and their mail must be somehow given to the ISP for delivery. This is solved in the following manner.

The administrator creates a new remote domain in FTGate called remote.users

He sets the delivery options to be the same as for the Outbox settings.

In Filter/Routes he creates the following routes

from: *
to: user1@a.com
route to: user1@a.com|remote.users

from: *
to: user2@a.com
route to: user2@a.com|remote.users

This tells FTGate to handle mail for those users differently and any mail for them will go into the remote.users remote domain and will be sent to the ISP. Mail for unknown users will go into the local domain and be handled by the domain settings.

This method prevents loops and allows the administrator to explicitly define which addresses are to be controlled locally and which remotely. Remote users can be added and removed by modifying the Filter/Route list.