During a setup change I had to temporarily move my incoming mailserver to Gmail and while I am now back in my own mail server, I again had this major headache of configuring the my DNS (using BIND) because I always forget the dots in the end of CNAME and MX records because usually I dont create nameserver records for external domains... So anyway here is the final configuration I used in Hetzners Domain Robot:
mail IN CNAME ghs.google.com. @ IN MX 1 ASPMX.L.GOOGLE.COM. @ IN MX 5 ALT2.ASPMX.L.GOOGLE.COM. @ IN MX 5 ALT1.ASPMX.L.GOOGLE.COM. @ IN MX 10 ALT4.ASPMX.L.GOOGLE.COM. @ IN MX 10 ALT3.ASPMX.L.GOOGLE.COM.