How to securely transfer a text file to site owner?

Not strictly a PHP question, but... I'm creating a site for a mortgage company that wants an online loan application. Needless to say, they're concerned about security, as the application includes social security numbers and various checking/savings/credit card account numbers. I'm fine with setting up the application page to utilize a secure connection. The thing I'm trying to figure out is how to securely get the information from the web server into the hands of the mortgage company. They need to receive it as a delimited text file that they can import into their loan processing software, but I definately don't want to transfer it as plain text. Ideally, the PHP script that receives the form data will somehow encrypt the information so that it can be emailed as an attachment without any fear of it being intercepted, but it needs to be a simple one-click process to decrypt it once the mortgage co has received it. I've considered several possibilities, such as putting the text file into a password-protected ZIP archive before emailing it, but haven't come up with a solution that I feel is sufficiently simple but still secure. Any ideas?