$MIMEobject->DESTROY;

The DESTROY method will get called automatically when the last reference to the object goes away, you shouldn't call it yourself and it won't do what you want. What you want instead is undef $MIMEobject; (or $MIMEobject=undef;, same thing), and you'll want to undef any other references to the object that you might have.

In general, you normally don't need to worry much about Perl's memory management, as long as you don't have circular references objects will be freed automatically when the last reference to them goes away. All that you have to make sure of is that you stop referring to the object.