What is rate limited proxy?

[Steve at Smartmailer]

When I check the open rate on my email campaign the IP address for some of the opens resolves to: rate-limited-proxy-66-249-92-29 There are a number of these in numerical sequence i.e 66-249-92-30/31/32
Does anyone know what this means?
Is it a bot of some kind as part of a security or anti spam set up? or is it a genuine open?

 

[Graybeard]

barry@paragon-DS-7:~$ echo 66.249.92.66
66.249.92.66
barry@paragon-DS-7:~$ ./ipinfo.sh
Pls enter your ip:
66.249.92.66
{
"ip": "66.249.92.66",
"hostname": "rate-limited-proxy-66-249-92-66.google.com",
"city": "",
"region": "",
"country": "US",
"loc": "37.7510,-97.8220",
"org": "AS15169 Google LLC"
that IP?

see: ASN-Blocklist - AS15169

 

[Steve at Smartmailer]

So it's a security block then?

 

[Graybeard]

maybe it's google (gmail) opening your images in your email? not sure--best guess?