Gmail provided by the paid Google Workspace service (formerly known as G Suite and Google Apps) has unofficial DNSSEC-signed MX records available for use. The officially supported ones that you’re told to configure do not offer DNSSEC signing.
These MX records have both IPv4 and IPv6 addresses, although the records are not officially supported or documented and may be unreliable or removed at any point. (I’ve been using them for a while now and they seem perfectly fine to me but use at your own risk.)
mx1.smtp.goog mx2.smtp.goog mx3.smtp.goog mx4.smtp.goog
The table below has the MX record and the A and AAAA record values.
mx1.smtp.goog 22.214.171.124 2001:4860:4802:32::97 mx2.smtp.goog 126.96.36.199 2001:4860:4802:34::97 mx3.smtp.goog 188.8.131.52 2001:4860:4802:36::97 184.108.40.206 mx4.smtp.goog 220.127.116.11 2001:4860:4802:38::97
I am using them myself but I am also willing to take the risk of them possibly vanishing without any warning.
kura.gg. 300 IN MX 10 mx1.smtp.goog. kura.gg. 300 IN MX 20 mx2.smtp.goog. kura.gg. 300 IN MX 30 mx3.smtp.goog. kura.gg. 300 IN MX 40 mx4.smtp.goog.