var prefix = "maith";
var suffix = "gazeta.pl";
var address = prefix + "@" + suffix;

document.write('<a href="mai');
document.write('lto:' + address + '"><img src="http://brafitting.eu/wp-content/themes/Jeans2c/images/mail.png" width="42" height="42" alt="Napisz do mnie" title="Napisz do mnie"></a>');