Hi Vinay,
The Content Filter Syntax can be specified as: (?i).*uc4\.example\.com
For a Message Filter regex you must use two backslashes so that after parsing, only one “real” backslash remains, thus the Syntax would be: (?i).*uc4\\.example\\.com
(?i) is used for Case-Insensitivity which can be placed at the Beginning of a case-sensitive regular-expression.
You can create a Dictionary as an alternative method in order to add the terms as mentioned in the query which could be used in any Content Filter / Message Filter.

Try to perform a Trace under System Administration and validate if it works as per your requirement.
Thanks,
Anand