This is a compilation of information I found in different postings on the net.

tmux can be invoked in command mode using tmux -CC. The simplest way to get a remote tmux session into a window of iterm is to invoke it on the remote host

   local> ssh rmhost
   #...
   rmhost> tmux -CC

This will open a new tmux session in a new iterm window.

To run tmux as the remote command argument to ssh, it need a pseudo-terminal attached. This means invoking ssh with the -t flag:

   local> ssh rmhost -t tmux -CC

If you want to re-attach to a remote session, you have to know its name. The easisest way to is to create a session with a well known name and re-attach to that session later. For that, we invoke tmux with the command new -A -s tmux-main. The session name is set using the -s flag, the -A flag specifies that new behaves like attach if the session exists. The command is now

   local> ssh rmhost -t tmux -CC new -A -s tmux-main

The final command we put together above is a much on the fingers if you use it a lot. The solution is either to set up a shell alias or a special Host configuration in your ~./.ssh/config file, as shown below in ssh--config. If you do that, the command to invoke becomes

   local> ssh tmhost

You might want to set up two shorthands, one for normal ssh accesses and one for ssh with tmux.