Thunderbird problem

Hi all, sometimes (infrequent) I am using Thunderbird to send e-mail folders from one user to another. At the moment it stops after a while, with this message: The connection was refused when attempting to contact live.mozillamessaging.com. What the hack?? The setup was pristine, accounts are internal ones.. the Thunderbird does not have any messaging configured (AFAIK). Why does Thunderbird want to connect to that server? How do I stop it? Thanks for answers Peter