I often rant about all that Asterisk can do. I have discovered some things it can't do though and I think it's important to disclose those.
I've been using JFAX/J2/jConnect for years to receive voice and fax messages (sent as e-mail). Their service went out recently so I decided to tackle getting Asterisk to handle faxes.
There's a great collection of information on the subject here.usually use Debian binaries but I downloaded Asterisk and the SpanDSP code. Lots of problems after that but here are the high points.
SpanDSP 0.0.1 doesn't seem to work with modern TIFF libraries. ftp://ftp.opencall.org/pub/spandsp/spandsp-0.0.1/README
N.B. Someone has reported that TIFF 3.6.1 has changed the headers a bit, and the following may not work without some changes. I will look into this.
I had TIFF issues. I tried the "whole" bundle.conflicted with existing TIFF headers.
SpanDSP 0.0.2pre versions don't seem to work with rxfax. ftp://ftp.opencall.org/pub/spandsp/spandsp-0.0.2pre4/README
If you want a stable version, don't use this one. The app_rxfax.c and app_txfax.c programs in this directory will only work with spandsp-0.0.2.
There is no "spandsp-0.0.2" (non-pre) as far as I can tell.
Bottom line...I didn't get it to work. I'm sure it can be made to work but I'm not up to it right now.
Someday I trust that this will be cleaned and added to Asterisk main. I'd happily put some money toward a bounty for it.