Earlier quoted context omitted.
Test messages to myself from Thunderbird and from gmail web interface did not get rewritten. How can I replicate this?
Send me an email at sneak@sneak.berlin and I'll send you my G Suite address that you can send a test message to that contains a URL, and I'll forward it back to you from my non-G Suite account so you can see what happens.
Perhaps some law enforcement agency has asked google to specifically track URLs in your messages and it's just you seeing this.