Being a fan of Thunderbird I was gutted when it started failing to download remote content. I followed all the suggestions to no avail. So I started trying both Inky and Mail Bird to compare. Both had their particular problems. Meanwhile I had backed up Thunderbird with Mozbackup and deleted all the emails addresses. Having become frustrated with the 2 alternative this afternoon I re-instated Thunderbird. On down;load email to my gratification and surprise it has started displaying remote content. I fit stays thus problem solved. I do so love Thunderbird, though I suspect a lot of that love may be familiarity as I have been using it for years.