WinFax SE was actually included in Outlook (I forget which prior version).
Winfax Pro integrates the same way by linking to the Outlook Address Book.
I think Winfax SE had you add fax@ before the fax number to have Outlook
trigger Winfax SE to handle the fax send.  Obviously Winfax SE handled the
fax receive.  I thought Winfax SE also let Outlook display the Winfax SE
folders but I don't see that with Winfax Pro.

I have Winfax Pro 10.0 (which is actually 10.01) and there were problems
with their "integration" which required you to get 10.02 but I wasn't about
to fork over more money to Symantec because what they sold in the stores was
defective (and, from what their rep said, was known to have the defect on
its release).  I think they are now up to version 11 but faxing is a
once-a-year event that I'm not going to spend much time to setup on my
machine.  The Fax Service in Windows XP is usually sufficient for the
occasional 1-page fax along with the Fax Printer to send a multiple-page
document through the Fax Service.  Installed WinFax Pro because of its Scan
and Send feature which presents a better looking fax to the recipient than
trying to scan into Word and print to the Fax Printer from there.

According to their help, "From Message Manager, you can send faxes as
self-viewing email attachments, ...".  So you can use Outlook to send faxes
and you can use WinFax's Message Manager to send fax attachments in e-mails.
Well, that certainly sounds like a lot of integration: Outlook Address Book
in WinFax, WinFax folders in Outlook, sending faxes from Outlook, sending
self-viewing fax attachments via e-mail from WinFax.  What other integration
do you require before Winfax is considered an product that integrates with
Outlook?