I do understand the scenario. With us, this is very unlikely due to the following reasons:
A. SAFENTRIX is a database oriented architecture and a replicated Database (Replication to ensure continuity in case one Data Center has issues) is used for Email scanning/blocking/delivery.
B. There is no manual intervention in any of the processes (even in setting up SAFENTRIX). You can try out now and you can setup SFX in less than 3 hours flat without requiring to contact anybody.
C. Because of the above, it is next to impossible for things to go wrong in your account alone.
D. Ofcourse, things change/go wrong (software needs upgrade, Hardware crashes, Connectivity goes down). In this case, redundancy comes into picture and rest of the Infrastructure handles the Email traffic. In case of Software upgrades, Rolling upgrade is done to avoid downtime. So while the individual components have issues, redundancy saves the day.
E. I am avoiding discussing the situation where the redundancy fails (this means a once-in-possibly-multiple-lifetime-disaster at multiple locations).
F. Then there is always monitoring. Test emails are sent in frequent intervals and their delivery checked for delays/congestion. Thus, we will know about problems before hearing from clients (and able to fix it by the time any body has the urge to try contacting us).
G. As far as specific emails being blocked/non-delivery is concerned, SAFENTRIX always allows a sender to get in touch with you (see Whitelist) and support would be quite unnecessary for the same.
And these technologies are fairly stable that I would think lot of the Security providers will have this.
Given this, it would be quite unnecessary to pick up the phone for support. And anyway, SAFENTRIX does provide Chat support.