Gmail provides SPF which describes valid outgoing IP addresses. You can use 'dig' or 'host' commands to fetch SPF records like so:
$ host -ttxt gmail.com gmail.com descriptive text "v=spf1 redirect=_spf.google.com" $ host -ttxt _spf.google.com _spf.google.com descriptive text "v=spf1 ip4:216.239.32.0/19 ip4:64.233.160.0/19 ip4:66.249.80.0/20 ip4:72.14.192.0/18 ip4:209.85.128.0/17 ip4:66.102.0.0/20 ip4:74.125.0.0/16 ip4:64.18.0.0/20 ip4:207.126.144.0/20 ?all" It shouldn't be too much trouble to script the lookups for you. In fact, I have a half-baked python script that you can use as a starting point: http://phxbsd.com/OpenBSD/mystuff/spf_whitelist.py -- Darrin Chandler | Phoenix BSD User Group | MetaBUG [EMAIL PROTECTED] | http://phxbug.org/ | http://metabug.org/ http://www.stilyagin.com/ | Daemons in the Desert | Global BUG Federation
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