I made this switch a few months ago.  It was straightforward except that, as Thomas says, you do need to get your ISP to set up a ptr record (also called a reverse dns record) for your fixed ip address before many recipients will accept you.  Do that before you make the switch.

Hello,

A brief overview of our environment is that it's predominantly Exchange and Outlook, but we use Mercury currently for some mailing lists as well as very large email blasts. We currently are using MercuryC so everything is going through our Exchange and Barracuda Spam Filter environment. Due to larger and larger lists(20,000 users) I want to separate Mercury from Exchange and Barracuda to stop the congestition that we're experiencing. Is there any special instructions that you would give me in this process? Also I am planning on getting a new external IP as well as a new MX record.

Thanks for any and all advice!!!

 Please ask any questions for more info about our environment! 

> A brief overview of our environment is that it's predominantly Exchange and Outlook, but we use Mercury currently for some mailing
> lists as well as very large email blasts. We currently are using MercuryC so everything is going through our Exchange and Barracuda
> Spam Filter environment. Due to larger and larger lists(20,000 users) I want to separate Mercury from Exchange and Barracuda to stop the
> congestion that we're experiencing. Is there any special instructions that you would give me in this process? Also I am
> planning on getting a new external IP as well as a new MX record.

You need to convert to MercuryE.   This means that you will require the Mercury system to have a fixed IP address, registered domain name and PTR record.  Once these are all in place all that required is to go to Configuration | Protocol modules and select MercuryE and restart Mercury.

I would recommend using VERP processing for the list mail to that you can control the bounces.