Domain names aren't "registered" with a server (they're registered with a registrar such as GoDaddy or Namecheap); while owning a domain is often bundled with server hosting or website hosting, they're really two separate services. So if you bought the domain at a webhosting provider, look for "DNS records" or a similar page, and see if the provider lets you directly edit the DNS data.
Most programs use the "address" (A & AAAA) records, which point directly to some server's IP address. For incoming mail, though, you need to add a MX record pointing to the SMTP server's name. For example, you should end up with something like this:
buggles.com. MX 10 myTestServer2.com. Though IMHO having a whole second domain for the mail server is somewhat overkill – it might be better to just add it as a subdomain of buggles.com:
buggles.com. MX 10 mail.buggles.com. mail.buggles.com. A 116.19.32.47 Everything else, though – things like outgoing SMTP, or IMAP & POP3 (for desktop mail apps), or webmail – is entirely up to you. If you want, you can go with the same mail subdomain as in the above example, and set up a webmail app at https://mail.buggles.com.