Laughing out loud, joking
This is more of an intuitive conclusion to come to than the other popular meaning of loljk, 'laughing out loud, just kidding', because we phonetically read words before processing possible acronyms.
Look I found $10 in the street! I'm rich! Loljk I'm really poor and desperate for this money.
邮件由 email@example.com 发出。我们决不会发送垃圾邮件。