What Countries does Google use to send Google Mail?

Question

I run an email server and can block IP addresses by country with my firewall settings. I am in the US. Unfortunately, some Gmail sent to email addresses on my server never got there because apparently Google used IP addresses from one of the blocked countries to send email (not from a US IP address). I'm not sure which Country it was. Is there a list of certain countries I should not block in order to receive email from Google? (when sending in the USA).

Answer 1

Posted same question at Google Groups and someone pointed me to this page that gives a list of data centers. I had been blocking Finland. https://en.wikipedia.org/wiki/Google_data_centers