say i use HUB role to route my emails to some gateway which would then shoot out emails to internet and vice-versa , is there really a difference it makes from using an edge role , in other words can i completely wipe out edge role from my organization and switch to HUB to perform all tasks of edge ..Would this be good approach..if so why and if not why not, please sugges

Nope , sounds like you already have mail gateway, introducing Edge would be "redundant" in my opinion and I see no reason for complication. Best design is "working" a simple one.

--oz

As mentioned by Oz, you can eliminate the edge role, just make sure you have some anti-spam\AV hygiene running on your HUB if your edge was doing it and if your gateway is not. 

are there any disadvantages of directly using hub to perform for edge role functions -say i do not use gateway and directly use hub in a topology wherein hub may not be exposed in DMZ but still sends and receives emails to & from internet  ?  

Hi Mediratta,

Based on my knowledge, I suggest using both Edge and Hub if you don't have Gateway deployed.

Officially, Exchange server can run well without Edge server, just running with anti-spam and anti-virus programs. However there are some anti-spam features don't exist in HUB server, I still suggest deploy Edge Server.

Following blogs for your reference:

1. Exchange Queue & A Edge and Hub Transport Roles, Virtual Machines, and More

https://technet.microsoft.com/en-us/magazine/2007.07.exchangeqa.aspx

2. Understanding Anti-Spam and Antivirus Mail Flow

https://technet.microsoft.com/en-us/library/aa997242.aspx

 

Thanks