As far as a method that’s already in place for a master account, there isn’t one.
It should be possible to script it so that copies are pulled from each E-mail address and placed into a master account, provided that each E-mail is also set up as a user (this give you ssh access to the E-mails). The script shouldn’t be overly complicated, but it’s not going easy either. Here’s the basics of what’s I’m envisioning:
Several E-mail address set up with users.
A bash script goes into the maildir at the end of every day (for example) and copies the E-mails to a directory in your “master account” You set up IMAP directories to keep track of who’s sending and receiving what E-mail.
Each time you need to add a new account or change an E-mail address you’ll also have to go in and update the script.
That’s the basics anyways. I have no clue what your skill level is when it comes to this sort of thing, but if you want a little help the wiki has some articles that will help you out - as well as google. Here’s some key words; SSH (access to the server), Bash Script (the coding to copy E-mails), Cron (the scheduler to have your script run on a regular basis), and IMAP mail directories.
Hope this helps, and isn’t too confusing.
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