Google dns mx-records
dns mx records are as follows:
aspmx.l.google.com / priority 1
alt1.aspmx.l.google.com / priority 5
alt2.aspmx.l.google.com / priority 5
alt3.aspmx.l.google.com / priority 10
alt4.aspmx.l.google.com / priority 10
for TTL, use 3600 seconds (1 hour)