Email is a very insecure way of sending information.
the only thing an SSL will secure is the site visitors connection to the Web Server.
Once the email is complied it is sent to the SMTP server, then the SMTP server relay's the message to the recipient, when the message is sent to the SMTP server, it will no longer be under the SSL layer.
Sensitive information should never be sent through email.
A credit application gets into some tricky waters as far as the web and electronic data transfer is concerned.
If you want to do this electronically, you will need to ensure that your server and database meet PCI Compliance standards.
the credit application information would be stored to a table in your database with the sensitive information stored using an encrypted format. to accomplish this will take a high level of web server, MySQL, PHP and PCI Compliance knowledge.
It would be easier to offer a printable pdf credit application and have them use standard snail mail to send it back to you.