Postbox Phishing Protection, and why Postbox makes network connections to Google
Postbox helps protect users from viruses, spyware, and trojan horses by checking URLs received in messages against a local database of suspected phishing or malware sites. The database is automatically updated every 30 minutes from Google's Safe Browsing Service, and if a potentially malicious URL is identified, a warning message will be prominently displayed.
To turn this feature on or off, go to Preferences, click the Privacy tab, then enable or disable "Block reported e-mail scams."
You may also need to open the Config Editor and type in browser.safebrowsing.malware.enabled and double click the row for browser.safebrowsing.malware.enabled to change the value from true to false. Then type in browser.safebrowsing.enabled and double click the row to change the value from true to false.