If I have understood your requirement correctly, you could use a SELECT() instead of LOOKUP()
Reason: Please refer article on LOOKUP() LOOKUP() is anyway a wrapper on SELECT() . 3 of LOOKUP() arguments may not have complex expressions. So you may not have CONTAINS() etc. within LOOKUP()
Finally your statement below means you have a column type list or enumlist that contains a list of emails.
if all above is true, then you could have a SELECT() statement something like below
ANY(SELECT(Table Name[ Return Column], IN( USEREMAIL() , [Email list Enumlist or list type column])))
Please replace USEREMAIL() with value to find if you have some other email to search rather than USEREMAIL(). Remove ANY() if your return value is likely to be spread acrosss many rows.