Here are some things to consider if your emails are not being delivered from a certain sender:

1. Verify that the sender’s email address is correct.
2. Check if their email provider may be delivering emails to your email program's spam or junk folder.
3. Check your email program if an add-on or third-party service is interfering with the incoming emails.
4. Ask them to add your address to their address book or whitelist of approved contacts.
5. Confirm if you’re not over your storage limit as some email programs won’t deliver emails to an address with an overfilled inbox.