Currently, when clicking the Configure GMAIL button, the following MX records are added:
ASPMX.L.GOOGLE.COM
ALT1.ASPMX.L.GOOGLE.COM
ALT2.ASPMX.L.GOOGLE.COM
ALT3.ASPMX.L.GOOGLE.COM
ALT4.ASPMX.L.GOOGLE.COM
It's worth noting that a correct SPF record is also required for proper GMAIL operation:
v=spf1 ip4:SERVER_IP include:_spf.google.com ~all
Therefore, I suggest that this record be automatically updated during the Gmail configuration as well.