Yes, 721r.org can receive emails.
Yes, 721r.org seems to be a legitimate domain.
A record
216.239.32.21
MX records
alt1.aspmx.l.google.com
172.253.122.26
alt2.aspmx.l.google.com
172.217.192.27
aspmx.l.google.com
172.253.63.26
aspmx2.googlemail.com
209.85.202.26
aspmx3.googlemail.com
142.250.13.27