<p>The conventional max is 3 times, mainly because a) your scores <em>usually</em> plateau by the third time and b) it seems obsessive to colleges that you're willing to/have time to take the SAT more than 3 times </p>
<p>But yes, theoretically, you could take the SAT as many times as you want</p>
<p>I don't know about registering by mail, but you could always register over the phone</p>
<p>My advice to applicants is to figure out what your target college is, and to take a look at the score ranges of the most recently reported admitted class. </p>
<p>From there, figure out what score you should aim for. (I recommend trying to get to or above the 75th percentile of the admitted class at the target college on each test section, knowing that not everyone will get to that level.) Then READ, READ, READ, and READ any kinds of books or magazines you like. (That's the best single form of preparation for all standardized tests: practice reading so that you read accurately and rapidly.) Be familiar with the test format through practicing with a genuine previous test under actual test time limits before you take the test "for real." Prepare well (get a good night's sleep) each and every time you take a standardized test. Quit when you reach your target score, or when you reach the highest score you reasonably think you can, and then devote yourself to other activities besides test-taking. Always take the test honestly according to the test rules. Never cheat. Don't forget to consider </p>
<p>And most of all, relax. Most people do better on tests if they treat them as interesting challenges (which they are) and not as life-and-death experiences (which they are not). </p>
<p>I took SAT twice, ACT once. I decided that after that excellent math score came in from the second SAT came in, superscored with the scores from my first, there would be no reason to take the ACT again.</p>