One troublesome technique finding favour with spammers involves sending mass mailings in the middle of the night from a domain that has not yet been registered. After the mailings go out, the spammer registers the domain early the next morning.
By doing this, spammers hope to avoid stiff CAN-SPAM fines through minimal exposure and visibility with a given domain. The ruse, they hope, makes them more difficult to find and prosecute.
The problem with this is that it causes some unfortunate and potentially nasty side-effects. During the interval between mailing and registration, the SMTP servers on the recipients' networks attempt Domain Name System look-ups on the nonexistent domain. The result? Delays, timeouts and other performance issues on the DNS servers.