Updated April 22nd, 2016
How to set different encryption levels in Serv-U without affecting existing users. This will suit if a single user requires stronger SSH encryption. Strong (2048 or greater) SSH encryption has an negative effect on performance but is more secure. This does not suitable for every user.
Serv-U all versions
Create a new Serv-U Domain
If the computer running Serv-U has only one IP address, the way to setup multiple domains is to configure each listener on each domain to listen on a different port (i.e. SFTP on port:222) to prevent listener conflict.
If the sole purpose of the new domain is SFTP, then open the relevant port on the firewall and allow only SFTP traffic.
Domain1 :22 > SFTP
Domain2 :222 > SFTP
You may set Domain level Limits and Settings > Encryption settings on Domain2 which will not impact Domain1
Domain2 will have a 2048 bits key and will only be used for its own domain.