On the Mac: enable remote login
# sudo systemsetup -getremotelogin
If the result if "remote login is off", then turn it on:
# sudo systemsetup -setremotelogin on
Now the users on the system are able to log in. You have to log in via your user name. But what is it. On the Mac try this in a terminal:
Then you can read your username, and log on:
# ssh email@example.com
Based on this article.
On the linux system
Enable openssh server, see this article. It's from Arch Linux, but here the actual distro does not matter, since we work in the terminal.
Concerning the systemsetup
Actually the systemsetup is a powerfull swiss knife for the system administrator. Read the man page.