I need to find out what all email ids among a list of 500 ids passed
in a single query, have been registered on my app. (Total registered
email ids may be in millions). What is the best way to store this kind
of data?

Should I store each email id in a separate row ? But then I would have
to read 500 rows at a single time ! Or if I use single row or less no
of rows then they would get too heavy.

Btw Would it be really bad if I read 500 rows at a single time,
they'll be just 1 column rows & never modified once written columns.