I’m no expert but it seems a mailbox actually is a user on its own, just restricted to the single purpose of e-mail, and its home directory is where your messages are stored and the server filters kept.
The convention for a mailbox is to setup the mailbox, then add an e-mail address and specifiy that messages sent to the e-mail address are to be delivered to the mailbox. However if you know the name of the machine handling your e-mail, you should be able to address messages to firstname.lastname@example.org, AFAIK it is impossible to do email@example.com
Hope this helps. I don’t quite understand your question. Perhaps it would help if you elaborate on your problem with recieving mail.
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