>(The receiving SMTP server is run by an ISP and I do not have access to their logs.)
It would appear to be most cost effected to pursue the ISP for non-delivery cause.
>Nobody knows what is going on with the actual inter workings of fax because you don't need to know.
Hmm, I read this as the fax got to the MFP and was printed. Then it failed to send the fax to some email account for archiving. The former is "magic", the latter should have logs.