Server move throws warning

[RichieBoy67]

Been awhile. I hope you are all well.

I am moving a client site from one server to another. It is 4.2.5 and running php 7.4.29..

I see a PHP warning in the diagnostic section when I send a test mail:

PHP Warning: sizeof(): Parameter must be an array or an object that implements Countable in ..../includes/class_core.php on line 4224

Test email sends fine. I didn't have these errors on the last server. Same version of php.

Thanks