Yes, ra3.us can receive emails.
No, ra3.us is a throwaway domain and should be blocked.
You can use MailCheck's free API to automatically block throwaway emails. Read our documentation to get started. No registration required.
A record
67.205.52.88
MX records
alt1.aspmx.l.google.com
64.233.186.27
alt2.aspmx.l.google.com
74.125.193.27
aspmx.l.google.com
74.125.192.27