It will be great to have T.38 fax support for hardware such as Dialogic (Formerly Brooktrout) and many others so that users can can send and receive faxes through Zimbra similar to MS Exchange (see this two-page MS fax implementation, it is currently improved in Exchange 2007 to also do per DID inbound routing; How to configure SBS fax ). Faxes should not only be deliverable per DID (not just per device) to several destinations but should be deliverable to deliver several destinations simultaneously such as shared folder, distribution group, email, printer, and database. This will enrich Zimbra's feature set in comparison to Exchange. Why applications like spandsp is not suggested is because it requires SIP, and unless Zimbra is a PBX, this may not be the way to go. So that is why a fax hardware will be needed such as dialogic fax boards which go over the PSTN. I will suggest to browse the Callweaver source code to see how they implement T.38, perhaps that will help or even be portable to Zimbra; wiki . callweaver .