example:epshetsky@test.com,
rek4@test.com,
rajesh1239@test.com,
mohanraj@test.com,
sam@test.com,
nithin@test.com,
midhunvintech@test.com,
karthickgm27@test.com,
rajesh1239@test.com,
mohanraj@test.com,
nithin@test.com,
I need results back like
epshetsky@test.com,
rek4@test.com,
sam@test.com,
nithin@test.com,
midhunvintech@test.com,
karthickgm27@test.com,
 
- sort line with Edit -> Line Operations -> Sort Lines Lexicographically ascending
 
- do a Find / Replace:
- Find What: 
^(.*\r?\n)\1+ 
- Replace with: (Nothing, leave empty)
 
- Check Regular Expression in the lower left
 
- Click Replace All
 
 
How it works: The sorting puts the duplicates behind each other. The find matches a line ^(.*\r?\n) and captures the line in \1 then it continues and tries to find \1 one or more times (+) behind the first match. Such a block of duplicates (if it exists) is replaced with nothing.
The \r?\n should deal nicely with Windows and Unix lineendings.
 
https://stackoverflow.com/questions/35329122/find-duplicates-and-delete-all-in-notepad