Based on the documentation at:
https://msdn.microsoft.com/en-us/library/office/jj250129.aspx
The Web App version of MS access has a completely different syntax for patterns.
Therefore a pattern for validating an email address is:
[FIELDNAME] Is Null Or [FIELDNAME] Like '%@%[^!,@,#,$,%,^,*,&,(,)]%.%[^0-9,!,@,#,$,%,^,*,&,(,)]%'
This is at best minimal validation, in that it validates that:
- domain name doesn't contain a limited list of special characters
- registrar doesn't contain numbers or a limited list of special characters