The Jargon File (version 4.4.7, 29 Dec 2003):

spamblock
 /spam'blok/, n.

    [poss. by analogy to sunblock] Text inserted in an email address to render
    it invalid and thus useless to spammers. For example, the address <
    jrandom@hacker.org> might be transformed to .
    Adding spamblock to an address is often referred to as munging it (see 
    munge). This evasion tactic depends on the fact that most spammers collect
    names with some sort of address harvester on volumes too high to de-mung
    by hand, but individual humans reading an email message can readily spot
    and remove a spamblock in the From address.

    Note: This is not actually a very effective tactic, and may already be
    passing out of use in early 1999 after about two years of life. In both
    mail and news, it's essentially impossible to keep a smart address
    harvester from mining out the addresses in the message header and trace
    lines. Therefore the only people who can be protected are third parties
    mentioned by email address in the message ? not a common enough case to
    interest spammers.