10.4 Subaddresses

Qmail provides each user with an unlimited number of subaddresses, which are the user's address followed by a dash^[4] and the address extension. Subaddresses are most useful with virtual domains, where qmail maps each address in the virtual domain to a domain-specific subaddress, but subaddresses are useful for regular users as well. Their primary use is for mail sorting. If you use a different subaddress for every mailing list to which you subscribe, you can use .qmail files to sort list mail into separate mailboxes or to reformat incoming mail. I also find it handy to use a unique subaddress every time I register on a web site so in case one of the site owners misuses the address, I know who to blame.

^[4] It's possible to use a character other than a dash, but I ignore that option for now.

Remember that subaddressed mail must be handled by a .qmail file or it will bounce. Here's a handy one-liner to put in .qmail-default:

| sed "s/^Subject:/Subject: [$DEFAULT]/" | forward username

It puts the address extension in the Subject line of the message to make it easier to see in your mail program. (It will also have a Delivered-To: line showing the subaddress, but most mail programs don't display that.)