You are using the wrong tool to solve your problem.

• Install MySQL
• Create a table with a email column
• Give the email column a "unique" constraint
• Import the file (just tell MySQL its a CSV file with one column)
• SELECT out the results into an newline delimited file

If you dont want to install MySQL, most any other DB will do (even Access probably). If the other DB doesn't allow uniqueness constraints on fields then just SELECT DISTINCT instead.

This might seem like alot of work, but if properly set up, you can use it over and over to process this file whenever you need to. Or you could just start using the DB instead anyway since it will make your life a lot easier anyway.

-stvn

Update: The more i re-read your post the more confused I am getting. Are these already in a database (RDMS)? Or is it in a text-file-database? If its already in a RDMS then just do a SELECT DISTINCT <column name> FROM <tablename> to get what you want, otherwise, see above. If you can't install the DB on the server, do it on your local machine and download the file. And for sure,.. don't do something like this with a CGI script, it will surely timeout no matter what you do.