To Connect with MSSQL or SQL Server via Zato 3:

#sudo su - zato
$/opt/zato/current/bin/pip install pymssql
(More info: http://pymssql.org/en/stable/intro.html)
$nano /opt/zato/env/qs-1/server1/config/repo/sql.conf

Add the following lines at the end:
[mssql+pymssql]
display_name=MSSQL
sqlalchemy_driver=mssql+pymssql
ping_query=SELECT 1

???I don’t know if this is required or not, but I still do it.
Deploy to other servers in the cluster:
$cp /opt/zato/env/qs-1/server1/config/repo/sql.conf /opt/zato/env/qs-1/server2/config/repo/

Restart your cluster and MSSQL should appear as an option under SQL Outgoing connections.