Like item returning Zend\Mail\Exception\InvalidArgumentException

Hi, I've done a fresh install of 3.3.14 from scratch (using composer) and getting Zend\Mail\Exception\InvalidArgumentException whenever anyone "Likes" a post.

I was running 3.3.13 on another machine without this error.

I have tried updated the pm.max_children in php-fpm configuration to 150, but I am still getting this on the screen.

The "Like" actually works. I have tried disabling the HTML Email Handler, Site Notifications and a whole load of other plugins but this didn't change anything.

Anybody have any ideas what is wrong please, the "like" is obviously a core feature so I assume the problem will be somewhere in my php config, but it is pretty much a default install just like the 3.3.13 version that works?  php version is PHP 7.2.34 Zend Engine v3.2.0.

I'm really struggling to see what could be the issue here, Many thanks in advance

(posted in the Elgg Chat too)

regards

Gary