The tarball must be placed in a public folder and the folder name must be called debian/amd64 and/or ubuntu/amd64.

Ex.
The URL of the server is: ftp://ftp.datanom.net/pub
The actual path is: /home/ftp/pub

The tarball must then be unpacked an placed under /home/ftp/pub so there now is a folder called debian/amd64 and/or ubuntu/amd64 with the contents of the tarball.

Users who whiches to be able to install via apt-get will have to add the following line to /etc/apt/sources.list

# claws-mail
deb ftp://ftp.datanom.net/pub/ debian/amd64/