When you need the literal IP addresses for Google Apps mail servers, start by using one of the common DNS lookup commands (nslookup, dig, host) to retrieve the SPF records for the domain _spf.google.com, like so:

nslookup -q=TXT _spf.google.com 8.8.8.8

This returns a list of the domains included in Google's SPF record, such as:
_netblocks.google.com, _netblocks2.google.com, _netblocks3.google.com

Now look up the DNS records associated with those domains, one at a time, like so:

nslookup -q=TXT _netblocks.google.com 8.8.8.8
nslookup -q=TXT _netblocks2.google.com 8.8.8.8
nslookup -q=TXT _netblocks3.google.com 8.8.8.8

The results of these commands contain the current range of addresses.

As of 5-15-19:

35.190.247.0/24

64.233.160.0/19

66.102.0.0/20

66.249.80.0/20

72.14.192.0/18

74.125.0.0/16

108.177.8.0/21

173.194.0.0/16

209.85.128.0/17

216.58.192.0/19

216.239.32.0/19

2001:4860:4000::/36

2404:6800:4000::/36

2607:f8b0:4000::/36

2800:3f0:4000::/36

2a00:1450:4000::/36

2c0f:fb50:4000::/36

172.217.0.0/19

172.217.32.0/20

172.217.128.0/19

172.217.160.0/20

172.217.192.0/19

108.177.96.0/19

35.191.0.0/16

130.211.0.0/22