Hi,
End of life announcement and migration options are provided in the below link:
http://www.cisco.com/c/en/us/products/collateral/security/email-security-appliance/eos-eol-notice-c51-730832.html
x70 appliances would continue to be supported till July 31, 2019.
It is recommended you contact your Sales representative to get details on migration to x80 models.
Thanks
Libin Varghese