Since DirectAdmin version 1.50.0 it is possible to have free SSL certificates for every user via Letsencrypt. As we at support secure data transfer, we have this enabled for every web hosting plan. Click here to enable free SSL certificates for your users. Click here to enable SNI on your server when you want SSL for every user without having a dedicated IP address for every user.

How to enable SSL for every user
Enabling SSL for every user is easy but the correct command depends on your Operating System. Therefore, make sure that the following command only outputs the usernames that exist in DirectAdmin:

ls -l /usr/local/directadmin/data/users | grep '^d' | awk '{system("echo "$9)}'

Change the number $9 until you see the usernames and use this number in the following commands.

Enable SSL for every user:

ls -l /usr/local/directadmin/data/users | grep '^d' | awk '{system("sed -i 's/ssl=OFF/ssl=ON/g' /usr/local/directadmin/data/users/"$9"/user.conf ")}'
Enable SSL for every reseller:
ls -l /usr/local/directadmin/data/users | grep '^d' | awk '{system("sed -i 's/ssl=OFF/ssl=ON/g' /usr/local/directadmin/data/users/"$9"/reseller.conf ")}'

NOTE: The reseller command may output something like "sed: can't read username/reseller.conf: No such file or directory". This is normal, as the command tries to find the reseller.conf for every user including non-resellers.

Congratulations: you have enabled SSL for every DirectAdmin user. Please keep in mind that the SSL certificates are not generated yet for every domain. This has to be done be the user self. Letsencrypt has a limit of 10 registrations per 3 hours which blocks the possibility to generate the certificates for every user at once.