It can take some time while GMail pushes a mail through your GrayList. The reason is that Google has several SMTP outgoing mail servers. The problem is that Google is rotating these mail servers to send even a single mail. Another complication is that Google SMTP mail servers does not have a single IP but they rotate several IPs for a single mail server. All these together does not make a good friend with graylisting systems.
Google can sometimes cause headache if you have a GrayList system implemented on your mail server.
What Graylisting does is that it records tripples: IP + sender + receiver.
When an email is sent from GMail, it is temporarily refused by our mail server (code 450 or 451)
Aug 13 16:29:14 ns2 policyd: rcpt=170846, greylist=new, host=22.214.171.124 (hs-out-0708.google.com), email@example.com, firstname.lastname@example.org, size=0 Aug 13 16:36:21 ns2 policyd: rcpt=170872, greylist=new, host=126.96.36.199 (wr-out-0506.google.com), email@example.com, firstname.lastname@example.org, size=0 Aug 13 16:56:04 ns2 policyd: rcpt=170914, greylist=new, host=188.8.131.52 (wx-out-0506.google.com), email@example.com, firstname.lastname@example.org, size=0 Aug 13 17:29:50 ns2 policyd: rcpt=170982, greylist=update, host=184.108.40.206 (wr-out-0506.google.com), email@example.com, firstname.lastname@example.org, size=0 # host hs-out-0708.google.com hs-out-0708.google.com has address 220.127.116.11 hs-out-0708.google.com has address 18.104.22.168 hs-out-0708.google.com has address 22.214.171.124 hs-out-0708.google.com has address 126.96.36.199 hs-out-0708.google.com has address 188.8.131.52 hs-out-0708.google.com has address 184.108.40.206 hs-out-0708.google.com has address 220.127.116.11 hs-out-0708.google.com has address 18.104.22.168 hs-out-0708.google.com has address 22.214.171.124 hs-out-0708.google.com has address 126.96.36.199 hs-out-0708.google.com has address 188.8.131.52 hs-out-0708.google.com has address 184.108.40.206 # host wr-out-0506.google.com wr-out-0506.google.com has address 220.127.116.11 wr-out-0506.google.com has address 18.104.22.168 wr-out-0506.google.com has address 22.214.171.124 wr-out-0506.google.com has address 126.96.36.199 wr-out-0506.google.com has address 188.8.131.52 wr-out-0506.google.com has address 184.108.40.206 wr-out-0506.google.com has address 220.127.116.11 wr-out-0506.google.com has address 18.104.22.168 wr-out-0506.google.com has address 22.214.171.124 wr-out-0506.google.com has address 126.96.36.199 wr-out-0506.google.com has address 188.8.131.52 wr-out-0506.google.com has address 184.108.40.206 wr-out-0506.google.com has address 220.127.116.11 wr-out-0506.google.com has address 18.104.22.168 wr-out-0506.google.com has address 22.214.171.124 wr-out-0506.google.com has address 126.96.36.199 # host wx-out-0506.google.com wx-out-0506.google.com has address 188.8.131.52 wx-out-0506.google.com has address 184.108.40.206 wx-out-0506.google.com has address 220.127.116.11 wx-out-0506.google.com has address 18.104.22.168 wx-out-0506.google.com has address 22.214.171.124 wx-out-0506.google.com has address 126.96.36.199 wx-out-0506.google.com has address 188.8.131.52 wx-out-0506.google.com has address 184.108.40.206 wx-out-0506.google.com has address 220.127.116.11 wx-out-0506.google.com has address 18.104.22.168 wx-out-0506.google.com has address 22.214.171.124 wx-out-0506.google.com has address 126.96.36.199 wx-out-0506.google.com has address 188.8.131.52 wx-out-0506.google.com has address 184.108.40.206 wx-out-0506.google.com has address 220.127.116.11 wx-out-0506.google.com has address 18.104.22.168