iptables questions

[JD]

I have instrumented my iptables to log all DROP'ed packets.
I have a huge plethora of packets dropped from these
3 IP addresses:
74.125.127.109
72.14.213.109
74.125.53.109
and all of them are from source port 995, which
is the secure POP3  port used by Thunderbird.
All 3 IP addresses belong to google.

nslookup reports
109.127.125.74.in-addr.arpa    name = pz-in-f109.1e100.net
109.213.14.72.in-addr.arpa      name = pv-in-f109.1e100.net.
109.53.125.74.in-addr.arpa      name = pw-in-f109.1e100.net

I am having no problems retrieving my email at all.
TB works just fine.
All 3 addresses belong to google.
Just do  whois 1e100.net

So why would the google mail server send me unsolicited packets?
As I said, I am having no problems sending/receiving email.

Cheers,

JD