Hi, Matt, thanks for replying so quickly. All contents of my old computer have been transferred to the new a couple of weeks ago and the old one emptied for resale. As mentioned, all seemed to be ok with the new computer for the first several days. I have used Thunderbird for a number of years on the old computer and never had the slightest problem. I've hired a technician, a fine one, but he cannot understand the problem either.