Admin Tools may not be the only plugin which sends emails on your site. That said, this is a warning, not an error.
The other problem I see in the site whose URL you have provided in the ticket is that you have restored a Joomla 3 site on PHP 8.1 or later which is barely compatible with Joomla 3 and most definitely not compatible with most of its extensions (our extensions are a rare exception; we support all PHP versions from 7.4 to 8.1 inclusive for use with Joomla 3). If you want to see what is giving you an error in the frontend, edit the configuration.php file and set the debug line to public $debug = true;
to turn on the site debugging information.
Basically, all the problems you have seem to come from differences in the PHP versions between the source and target site. Do keep in mind that Akeeba Backup CANNOT and WILL NOT rewrite the source code of Joomla and its installed extensions to magically make them compatible with the PHP version of the target server. You need to ensure that the PHP versions match when transferring your site.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!