After you confirmed what @sdayman said, if it is still not working, consider this
Delete any MX records that are pointing to eforward*.registrar-servers.com.. You may still have some old records from the built-in email forwarding of namecheap which aren’t remove so your email is sending to their email forwarding service, instead of their private mail service. These two are different.
Also, let us know your domain, it’s easier to support once we know your domain and can tell imediately if something is off the chart