At times it would not only be nice but also might be necessary to have the ability to locally deliver mail for a domain as well as forward those same mail messages to another domain (migrations to other services, &c). How does one go about configuring postfix in such a way that fulfills these requirements?
Luckily the BCC field of e-mail allows us to accomplish this quite elegantly. The postfix parameter we'll take advantage of is recipient_bcc_maps. By setting this to a regexp lookup table, we're able to add a BCC to all messages destined for a particular domain passing through this instance of postfix:
recipient_bcc_map = regexp:PATH
After we've added the above to our postfix configuration, we still need to create the regexp mapping file with lines similar to the following:
Setting up a deliver and forward configuration on postfix is very simple and requires little consideration about the mail delivery process itself.