I have several domains with dynadot all using dynadot's name servers and email forwarding to forward from certain emails to my gmail address. I recently purchased a domain name from an international registrar (.tt) which does not offer this feature so I was wondering how it works so I could set up something similar on my own server. Most support I find about email forwarding to gmail involves setting up a smarthost which requires setting up certificates and having the server login to gmail using my credentials. I know this isn't the case with dynadot's email forwarding as I never had to give it my gmail credentials.
You would need to set up a mail server, for example, qmail is a good one. You could then set the MX records for the domain to point to the qmail server. Once you do that, you can set up email forwarding in qmail.