Last week the openssl project issued a security advisory, and the updated package was released from Ubuntu yesterday. It's unlikely that the security issues would affect Mail-in-a-Box boxes, but for good measure you should make sure the updated package is installed.
Your box should have automatically installed the package last night, depending on what timezone your box is configured in, but a reboot of the box is likely necessary anyway --- which you'll need to do manually.
Log into your machine with SSH (as you did when you created your box).
You can check if the updated package is already installed by running:
sudo dpkg-query -W openssl
The updated package is:
openssl 1.0.1f-1ubuntu2.16 (ends in 16)
The insecure package is:
openssl 1.0.1f-1ubuntu2.15 (ends in 15 or lower)
In either case, take this opportunity to update all of the system packages:
sudo apt-get update && sudo apt-get upgrade -y
And finally reboot:
Wait a few minutes, and then everything should be back running again.