Sending print jobs by e-mail does not work because Printfil requires Outlook while I use another mail client.
Printfil does not necessarily requires Outlook. It can use any MAPI compatible e-mail client (Outlook Express, Mozilla Thunderbird, Microsoft Mail, and many others)
If Outlook is invoked to send mail instead of the e-mail client you're used to use on your machine, is simply because Outlook is installed and Printfil detects it, but it's not configured to use the default MAPI client instead.
In order to have Printfil automatically invoking your MAPI compatible mail client just open the Printfil's configuration dialog, and put a check mark near the "MAPI" option in the "PDF & E-mail" tab.
Alternatively you can avoid using any mail client at all by setting up Printfil to send out e-mail messages through a SMTP server directly (please search for the "EMailClient" word at Chapter 4: "Miscellaneous Options").