You can just turn off deprecated messages in your php.ini file, or on the top of any page that is experiencing this issue for now.
https://stackoverflow.com/questions/24559842/turning-off-deprecation-warnings-in-php-ini-file-wamp/24559940
In the long term - this is a warning that the code on your page is a decade old and will eventually not be supported, so you wouldn't want to update your php version or it could cause issues.
The long term solution is to purchase DataBridge v2 and re-apply the validation toolkit and email functionality to update it to modern standards.