Yeah when I worked at Deloitte Consulting, we had similar training that said something to the effect of "don't put something in an email that wouldn't feel comfortable as a newspaper headline".

"assume your mother, and/or the courts, will read it." was the version I heard

"Remember: the e in e-mail stands for evidence."

Were you told this literally?

It's a common joke, but it's not something you would find literally in the Google-internal official material. They ain't that stupid.

The joke ain't Google specific, I might have picked it up working in finance. If you bing the phrase, you'll find plenty of hits in published articles.

And the O in RTO stands for Oral-communication-only

And the s stands for secure