Why didn't I receive any IPN posts?

You haven't been receiving Instant Payment Notification (IPN) posts.

Causes and Solutions
Multiple issues, explained in the next few paragraphs, can produce this error. Your receiving account's email address is unconfirmed
Check that you've confirmed the email address on the account the payment is being sent to. For profile-based IPN, the email address on the receiving account must be confirmed, or else the IPN won't be sent to your script. IPN is disabled in your profile
If you use profile-based IPN, check that it's not disabled in your account profile. Here's how:

  1. Log in to your PayPal account.
  2. Click Profile. (If you don't see Profile on the top right, navigate to My Account > Profile > My selling tools.)
  3. Select Profile and settings.
  4. Click My selling tools.  
  5. Click Update next to Instant payment notifications.
  6. Check that IPN is set to Enabled.
Your firewall is blocking IPN
Instant Payment Notification is an HTTP POST initiated by PayPal. If you have a firewall on your server, check that it's not blocking the post from PayPal. For help resolving this issue or others, visit PayPal's Contact Customer Service page.

See also:
Instant Payment Notification Developer Guide
Instant Payment Notification Simulator