I'm not receiving copies of my own posts
First, make sure you have 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, this behavior is by design – Gmail doesn't show you mail you sent to yourself and expects you to find your message in your Sent box. Your original post will be visible on replies. There's a way you can work around this with a filter but your mileage may vary.
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.
If you're a Gmail user and you're expecting to receive a copy as confirmation that your post made it to the list, you could turn on the ACKPOST flag and you'll be sent a separate notification when you post.