WISP and client security - portal or Gmail

[strongsilence]

For fear of allowing clients to divulge sensitive tax information, then blaming it on me, I have decided to force clients to choose using Gmail and texts for transmitting information or using my portal solution, which is Citrix ShareFile.  It has meant adding a paragraph and decision boxes to my engagement letter, then setting up a ShareFile account for each client that opts in. It is a laborious process, and I often am happy that they opt-out.  

Looking for easier solutions.

Adding a line to my signature would not protect me, although IANAL.  Currently, the language is this

This email may contain confidential tax or financial information intended only for the recipient. If you received it in error, please notify me immediately and delete it. For your security, do not email Social Security numbers, IRS Identity Theft Pins or other sensitive information.  I will never request (and you should not act on) changes to payment instructions or banking information based solely on email. Please confirm by phone using a known number.

[Terry53029]

I never have clients send anything tax related through e-mail. I use Encyro for all tax related matters