Microsoft Exchange is not required if the Avaya documentation is correct. Smaller businesses may use an SMTP server instead of an Exchange server. There is a section "Using the Unified Messaging Application with an SMTP Server" starting on page 20 of the Unified Messaging Application Installation and Configuration Guide that should be useful. I haven't setup Partner Messaging with an SMTP server and so I hope that this information publish by Avaya is correct and helps.
This guide can be found at
https://support.avaya.com by clicking on "Installation, Migrations, Upgrades and Configurations" then clicking on "PARTNER® Messaging" then clicking on "Unified Messaging Application Installation and Configuration Guide" and finally clicking on the file type that you want: PDF or ZIP.
Please let us know how this works out. Thank you.
-Rob
