... by accepting TER's Terms of Service Agreement.
The way I read TER's privacy policy (see link), TER reserves the right to use your personal information under certain circumstances:
"CONFIDENTIALITY AND SECURITY OF PERSONAL INFORMATION. Except as otherwise provided in this Privacy Policy, we will keep your Personal Information private and will not share it with third parties, unless such disclosure is necessary to: (a) comply with a court order or other legal process; (b) satisfy our legal obligations to cooperate with law enforcement or other investigating agencies; (c) satisfy any laws or regulations, or, governmental or legal requests for such information; (d) protect our rights or property, or the rights or property of others; or (d) enforce our terms of service Agreement."
Note especially the last exception. How I read that is, if you are suspected of violating TER's terms of service agreement, TER Admin could access personal info to investigate.. PMs aren't specifically mentioned anywhere in the Privacy Policy, but I think it's reasonable to conclude they are considered "personal information".
It's not clear from the privacy policy that PMs are stored in encrypted form. They are transmitted to/from TER in encrypted form if encryption is enabled on your device, as it is on mine (i.e. HTTPS). If PMs are not encrypted on disk, anyone with access to the server including TER Admin could potentially read them. TER states that they take measures to protect data, but as we all know almost any server can be hacked with enough skill and effort.
It would be great if Admin would confirm or correct my analysis on this question.