Hosting Admin: Catch-All
March 12, 2004
Modern hosting accounts have a "catch-all" feature. Be
default, there's an alias "catch-all" pointing to the "admin" account.
When someone email to a non-existent address, due to typo or account
deletion, it'd be forwarded to the built-in "admin" account. Spammers
are now known to send email to generated addresses, such as: resume@
sales@ info@ joe@ mary@, etc. In other words, they carpet bomb a domain
in hope of hitting a recipient.
1. Active, attended Catch-All. Leave catch-all alias active. Routinely
login to admin account to process the stray legitimate email, notify
senders or simply forward to the rightful recipients, and finally,
delete the remaining junk. Failure to do so will result in junk mail
eating up valuable space quota.
2. Disable catch-all feature by simply deleting the catch-all alias.
This strategy is known as "bounce." All email sent to non-exisitent
names will be bounced back to sender along with a notice. That means
your mail server will send a copy of the inbound message (with
attachments and all) to the return address, for each and every bad
inbound recipient name! This could potentially incur significant
bandwidth. For the average business, the bandwidth allotment is high
enough (relative to actual usage) that it's a moot point.
3. Blackhole Catch-All. Delete the built-in alias to admin. Recreate a
new Catch-All alias to email@example.com. Sender will not
receive any notice of invalid addresses. This is considered appropriate
and is common practice nowadays.
As of March 2004, the Bravo recommended option is #3. For those sites
where we assume the role of administrators, we implement option #3 by
default, unless otherwise specified.
#1 requires too much efforts if you receive astronomical amount of spam.
Some people forward it to an existing user account (instead of admin,
#2 is VERY dangerous! Bouncing is considered inappropriate and
counter-productive nowadays. 99.9% of mail with bad inbound addresses
use SPOOFED return addresses. Most likely, your bouncing will:
a. serve as "mail bomb," exploding the innocent victim's mailbox, whose
address happens to be used by spammers as return address. Or,
b. become "accidental spammer" sending massive amount of email to
non-existent addresses, which in-turn trigger a perpetual storm of
double-bounce notices, etc.