.CYOU TLD - We See You Too Spammer

ShortDot SA, the top-level domain registry that brought us the infamous .ICU TLD is back with yet another useless domain extension. Say hello to .CYOU TLD, the “savvy and uber-cool domain”, at least according to ShortDot.

.cyou spam domains

An inbound mail server rejecting email spam from .cyou domains.

In my experience, the majority of the new top-level domains like .cyou are launched by companies wanting to make some quick and easy cash. When they eventually learn that nobody is interested in their new domain, the price gets dumped and spammers move in for the kill.

I would strongly encourage anyone looking to buy a domain name to go with one of the old and established generic top-level domains. Getting a domain name for 1$ with Namecheap might sound like a good deal, but it’s not worth it in the long run.

How to block spam from .cyou domains

You had me at ShortDot SA.

.cyou is owned by ShortDot SA

Block spam from .cyou domains with Postfix

With Postfix, you may add or edit /etc/postfix/reject_domains to identify .cyou domains using a simple regular expression:

# /etc/postfix/reject_domains
/\.cyou$/ REJECT We don't talk to .cyou domains

Proceed to edit the main Postfix configuration and append the regexp lookup to the smtpd_sender_restrictions policy:

# /etc/postfix/main.cf
smtpd_sender_restrictions = pcre:/etc/postfix/reject_domains

Reload Postfix to activate the new configuration.

Block spam from .cyou domains with Sendmail

With Sendmail, you may use the access database to reject messages from .cyou domains. Simply edit /etc/mail/access and add a reject statement at the end of the file:

# /etc/mail/access
cyou  ERROR:"550 We don't talk to .cyou domains"

Finally, we’ll use makemap to rebuild the access database with the following command:

makemap hash /etc/mail/access.db < /etc/mail/access

All in a day’s work.