If you suddenly cannot send nor receive after an update then it is likely your Firewall is blocking thunderbird.

note the latest update 45.1.0 was released on May 10th so it is highly possible that the update not being recognised by Firewall.

Close thunderbird. Access Norton and make sure thunderbird is set to allow. Note: on one occasion, I had to block TB, ok it and then go back into Norton and set it to allow. Norton is notorious for seeing new updates as if a new program. Restart Computer and then thunderbird.

Disabling Norton Firewall is not going to fix because then the default Windows Firewall kicks in and is likely to be blocking it as well.

Thank you for the advice. I will try it, but as I have disallowed TB updates and am still using 38.0.1 - as I said in the question - I'm not sure why Norton would have assumed TB had been updated.

I'll post another reply when I've tried your advice.

Hallo again Toad-Hall. Thanks very much indeed - it worked !

I'll now try reinstating in TB the email address/account I previously deleted in my unsuccessful frenzy.

Thinking further: Your explanation has now made me wonder whether my adherence to TB38.0.1 is any longer necessary; maybe it was the same problem of Norton super-diligence which caused the blockage before ? If so, perhaps I should install the latest version of TB since it presumably has other benefits I don't realise I'm missing ?

Updating does have some benefits:

• https://www.mozilla.org/en-US/thunderbird/45.1.0/releasenotes/

Before updating, I would like to draw your attention to two specific changes. 1. A new 'Correspondents' column header has been created. It effectively replaces 'From' and 'Recipients' column headers and is really useful if you keep 'Received and Sent' emails in th same folder. From and Recipients column headers are still available. There is much on going discussion at this time on improving this:

• https://bugzilla.mozilla.org/show_bug.cgi?id=1266126

If upgrading to version 45.1.0 : The changes are not set as default, so you should see same as before with the option to use Correspondents column header.

If upgrading to version 45.0: 'Correpondents' column header is set as default and completely resets all the various preset column headers in all folders meaning a manual fix if you do not like what is presented. One method of stopping the auto change is to modify a Config Editor setting prior to upgrading or reinstalling version 45.0

'Tools' > 'Options' >'Advanced' > 'General' tab click on 'Config Editor' button Tin top search type: correspondents. Look for: mailnews.ui.upgrade.correspondents double click on that line to toggle the 'True' to 'False' close window - top right X click on OK

More info on correpodents column:

• https://support.mozilla.org/en-US/kb/new-thunderbird-45#w_message-list-and-message-header

2.Write window when composing now defaults to 'Paragraph'. This will mean when you press 'enter/return' key, it will leave a blank line, but it is possible to turn off Paragraph as default and revert to 'Body Text as default which still goes to next line. Info here:

• https://support.mozilla.org/en-US/kb/new-thunderbird-45#w_mail-composition

Thanks again Toad-Hall. I'll look at the info you have given, and the detailed effects/benefits before updating. I'm content to close this enquiry chain now, as I may not have time to do more for several weeks.