The mainstream license is required for the following features only:
Reach Me
Notify Me
Text message or page notification
Phone call to a telephone or mobile phone
E-mail copy
Fax
Detect and transfer to fax server
Receive and forward to e-mail
IMAP access to the Avaya message store
Speech based features
Speech recognition for addressing
Basic Speech Auto Attendant
Access to Avaya one-X® Speech
Except the listed features, all other features of the Messaging system do not require a mainstream license.