424859 PHP CSV file importer fix... 2

I have a PHP email script that lets users upload a csv file and it imports email address and any other data on the file. For some reason when you import more than 10000 lines/leads from the csv file it won't send or create a message to be sent out it just disappears when you click send or load up message. I need it to be able to handle at least 25,000 lines...If it needs to be done a different way that is fine..just so long as it checks the blacklisted emails before going out. Along with that it currently gets the column titles and lets the user select them from a pull down menu...I want to change that to show them as links that would insert it to the subject or body when clicked. Currently there is a text radio button a HTML for the user to select the format. I would like to instead have an html editor in place but with the ability to still send only text too. Question please ask...