How about bcc all mails to another account as mail archive/backup? for example, bcc all mails sent by or delivered to user@domain.ltd to user.backup@domain.ltd?

I did the same, it works, but I found the duplicated emails when I download all email from the backup account. for example. user1 sents an email to user2, in backup@mydomain.com account will receive 2 same emails. i know this should be reasonable, but when user1 to 100 users in the same domain, the backup account will receive 100 same emails. is there any way to only keep one email for this kind of situation?

thanks for reply. I found one tool to remove the duplicated emails from outlook.
http://www.vaita.com/ODIR.asp
but this needs to download all emails to outlook, this job takes too much time, I am thinking of one script or tool to do it in server. like sieve filter, or the tools in webmail.
this function is really important for my company. I will appreciate if you could help. thanks

thank you very much.
this helps me a lot currently.
I found one article that says it's possible not to deliver duplicated email to backup account. but I didn't try it successfully.
would you mind spending a little time on this article and show your option?
http://readlist.com/lists/postfix.org/p … 88452.html
thanks again.

yes. I found that setting receive_override_options=no_address_mappings in master.cf. when I bcc all accounts' email to backup@domain.ltd. i still get a lot of copies.
but when I put it in main.cf. nothing I can get in backup account.
seems the current solution is only to use the script you mentioned from that website for a while. do you think so?