I'm not receiving copies of my own posts
First, make sure you've got the “ECHOPOST” flag set for your subscription (this can be done in the Web Login). This is a default setting when the mailing list you're subscribed to was created, but the list administrator(s) can opt to turn it off.
Next, if you're a Gmail user, see this Gmail Product Forum thread. It's possible other mail services do this sort of thing as well, so as long as you're able to receive others' posts, check with your mail provider to make sure they're not storing messages someplace unexpected.