8.3 Google reserves the right (but shall have no obligation) to pre-screen, review, flag, filter, modify, refuse or remove any or all Content from any Service. 11.1 By submitting, posting or displaying the content you give Google a perpetual, … free … licence to … any Content. 17.1 [a]dvertisements may be targeted to the content of information stored on the Services, queries made through the Services or other information.Yahoo TOS:
6. You acknowledge that Yahoo! may or may not pre-screen Content, but that Yahoo! and its designees shall have the right (but not the obligation) in their sole discretion to pre-screen, refuse, or remove any Content….And from the ABA Model Rules of Professional Conduct:
Rule 1.6. (a) A lawyer shall not reveal information relating to the representation of a client unless the client gives informed consent ....So beyond the security concerns, it appears that the use of popular, free email services for client communications is a violation of ethics rules since lawyers are revealing client information to a third party. If you didn’t have enough reasons for moving to a secure email address on a domain you own, you can now add “getting a letter from Discipline Counsel” to the list.