MX records not showing my subdomain

[twineee.rf.gd]

I am trying to add SMTP to my site, but when I go to the page, it doesn’t show my subdomain:

However, my domain does seem to exist on my VPanel account:

[KangJL]

You will need a custom domain to do that

[twineee.rf.gd]

Is there no way to use email on a free subdomain?

[Meishin]

There no longer is