I have one similar problem. For some reaseon, after backup, I lost the fax configuration. Finally I must to do a hand configuration. Now works, but email with fax come from Fax Elastix<email@example.com>. I have the domain well configured at the end of main.cf with mydomain and myhostname. Emails from command line goes out with correct domain but emails from fax no. Etc/hosts is correct too. Where must I change de domain for faxes? Thanks.