I am perplexed

I've been using smarteremail for a while now and I find a lot of features that are useful to me, but every now and then I find some things that I miss compared to other mail servers. Smarteremail is very configurable and I think some things should be added.

Here is the scenario I can't replicate with smarteremail


Domain xxx.tld

manages
user1@xxx.tld
user2@xxx.tld
user3@xxx.tld
user4@xxx.tld


For line speed needs, the customer decides to install a version of smarteremail on a local server but which he will only have to manage

user1@xxx.tld
user2@xxx.tld

Basically it downloads the messages from the main server with remote account for user1 and user2

What happens if user1 decides to send a message to user3@xxx.tld


With other servers I had the possibility to set the local server as a backup, set the fact that if a message is sent to an unconfigured @ xxx.tld user it must forward it to another server
mx.xxx.tld

And this happens at the SMTP level. Using the catch all addresses would become all complicated and in any case it would not work correctly if the destination addresses are more than one or even in bcn

Here is a typical configuration on another server

I assure you that I have been using it for years and it works great

In practice it behaves like this
If it finds a user locally, it delivers the message, if it cannot be found it forwards it to another server