Hi Stefano
Thank you for your response. Max-memory is 128M in php.ini for the site, and wp-config.php, apache2 restarted, now showing the 128M.
Newsletter set to debug=on, and Error reported as follows, sensitive part redacted.
[20-Feb-2017 10:31:51 UTC] PHP Fatal error: Cannot redeclare class phpmailerException in /home/xxxxx/public_html/shop/wp-includes/class-phpmailer.php on line 4040
I have restarted Apache, so a little lost on this one.
Best regards
Nigel