Validating Input Email Address via regex

Hi Experts,

We have a requirement to validate Input email address for External Partners to be an email address from non-client domain.

Planning to validate the same using regex in 'Validation' tab of custom attribute 'Z_TEMP_EMAIL_EXT', mapped to the UI task used for External User ID creation.

Client has two email domains, namely 'FN.LN@clientabc.com' and 'FN.LN@xyzclient.com'

I have arrived at below regex for validating the client domain; and attempts to ensure these are NOT input (negative condition) are not working.

Please suggest how to validate regex for NOT including these domains. 

(1) "^(.*)[\@](clientabc|xyzclient)[\.](com)"

(2) "^(.*)[\@](clientabc|xyzclient)[\.](.*)"

(3) "(\Qclientabc\E)|(\Qxyzclient\E)"

With Regards,

Ganesh.S