Inevitably your email address will be somewhere on the web and a web bot will scan that webpage, extract the emails, and add them to a big list for spammers. In response, some people spell out their email address like “trnka at udel dot com”.
I imagine people view it as a deterrent – bots can grab the majority of email addresses even without processing for spelled-out ones, so there’s little benefit to adding processing. At the same time, it only takes a few minutes of fiddling with regular expressions to parse most of the spelled-out ones, and I’m sure it would have a very low false-positive rate.
|addr = decodeURIComponent("%74%" + "72%" + "6E%6B%61%" + "4" + "0%75%64" + "%" + "6" + "5" + "%" + "6" + "C" + "%" + "2" + "E" + "%" + "6" + "5" + "%" + "6" + "4" + "%" + "7" + "5")|
|document.write("addr + "\">" + addr + "")|
In some sense, the practice of trying to hide your email from scanners is moot – if bots grab emails from PDFs, there’s nothing I can do about my published papers. Similarly, I can’t do much about hyperlinks on departmental webpages or other types of lists. At the same time, it’s plausible that maybe someday in the distant future, Apache might change any mailto link into a random code generation (more random even than what I’ve shown).