<?php

$testes = [
    "000.000.000-00",
    "00000000000",
    "000",
    "usuario@servidor.com"
];

foreach ($testes as $teste) {
    if (preg_match("/^\d{3}\.?\d{3}\.?\d{3}-?\d{2}$/", $teste)) {
        echo "É CPF", PHP_EOL;
    } else {
        echo "É e-mail", PHP_EOL;
    }
}