The Massachusetts and Nevada PII laws require all email with SSNs or other personally identifying information to be encrypted (TLS or otherwise).
Of the free email providers, GMail does support TLS but they also index the message contents to provide contextual advertising through AdSense.
If we were to recommend our clients of Hotmail (doesn't support TLS) to use GMail, we also want to include instructions on how to opt out of whatever indexing is done within the GMail product.
What procedures need to be followed to ensure that a GMail user's PII data is protected and not published into any index?