For $ 10/month (less if paid on an annual basis), MyFax provides such a confirmation email as well as such reliable service that I jettisoned my standalone fax and dedicated line 11 -- yes, eleven -- years ago. MyFax assigned me a toll-free number, which helps persuade chintzy clients and their employers to fax me when necessary. I'm authorized to send faxes from more than one email address -- I scan everything into PDFs in my office and simply attach those to a standard email address that begins with the recipient's fax number.
Not only that, but whenever I've had a problem such as an unreceived fax I've been able to reach live, human tech help no matter the time -- and a couple of times they conducted technical tests on my line and the recipient's. I've never exhausted the limits on outbound and inbound faxes, which I just now looked up and found to be 200 pages in and 100 pages out per month. There is an online resource such as LionEA described for eFax, which I've used to find faxes from YEARS ago -- apparently no limit on storage.