even with mail.mydomain.com defined (without DNS and MX records, just for mydomain.com) it does not work. Mail is not relayed to MX records with lower priority (<90) which are google.com urls.
pri.mydomain.com looks like
MX 90 mail.mydomain.com.
MX 40 ASPMX3.GOOGLEMAIL.COM.
MX 40 ASPMX2.GOOGLEMAIL.COM.
MX 20 ALT2.ASPMX.L.GOOGLE.COM.
MX 20 ALT1.ASPMX.L.GOOGLE.COM.
MX 10 ASPMX.L.GOOGLE.COM.
mydomain.com. A 111.222.333.444
www A 111.222.333.444
mydomain.com. TXT "v=spf1 a mx ptr ~all"
do I need A record for mail.mydomain.com?