How do you allow postfix subdomain mail delivery?

[shdwdrgn]

I have multiple servers on my network receiving emails, and each one is set to receive messages at domain.com, mail.domain.com, and mx?.domain.com (currently running mx1 and mx2; the new ispconfig3 server is designated mx4). Server is Ubuntu, SMTP is postfix. Incoming emails generate the following log:

... postfix/local[10524]: E4D3B21265: to=<bogey@mx4.domain.com>, relay=local, delay=0.29, delays=0.11/0.09/0/0.1, dsn=5.1.1, status=bounced (unknown user: "bogey")

Note that the mailbox bogey@domain.com has been created and will accept emails. So this is a two-part question, and I'm hoping there is an easy answer...

1. A way to tell ispconfig that emails to user@domain.com will also be accepted at user@mail.domain.com
2. A method of designating that this particular server will also accept emails to all virtual domains that are tagged with this server's mx -- thus emails received for user@mx4.domain.com and client@mx4.example.net would also be accepted.

Question #1 is the most important part I am focusing on, since #2 can be worked around with an easy solution to #1. I can post my config files if needed, but I don't believe this is a configuration issue. Postfix seems to be working as instructed (only allowing emails to known addresses), I just can't figure out how instruct it to allow the subdomain aliases.

[till]

Add mx4.domain.com as email domain in ISPConfig and then add email addresses or aliases for the domain mx4.domain.com

[shdwdrgn]

So I'm just supposed to create a copy of every user's mailbox for every mx subdomain (and yes, there are reasons why the emails will get the mx tacked onto the address)? Assuming I were to do this, how then do you propose I get all of the received emails back into a single mailbox for the user to read?

I've been using LDAP records for years. Under postfix, I have a query that picks up associatedDomain values for each domain, then allows emails for all users under this domain to also come in under the addition domains or subdomains. I was really hoping to find something straightforward like this to easily expand on the accepted subdomains of all users under a given domain.

[till]

Nobody is doing this as nobody is receiving emails on their subdomain. This catches just more spam and I've never seen that someone is sending emails to user@mx4.domain.com instead of domain.com. But you can use the same setup that you used with ldap for ispconfig too, its just a plain virtualuser setup.