Hello, I'm a voip specialist with 10+ years of experience working on the TS department of a VoiP company; I can install, troubleshoot and customize many VOIP devices including: softphones, ATAs, IP-phones and PBX systems. I read your project description, at it sounds to me more like an issue with your mail server holding the e-mails back for some reason, I can check your mail server and run some tests to pin-point what is going on, but I'll need ssh and root access to the fusion/freeswitch server. I'm available to talk through chat.
Thank you.