The only way you can know if an address is valid is if the recipient confirms that it is valid. Otherwise, you have to check that the domain exists, accepts mail, and does not reject or bounce the message. There is no general purpose way to do so without attempting to send the message. Even then the server may not bounce the message to thwart dictionary spamming attacks.

Perhaps the mail id 'fefsdfdsf@gmail.com' exists and the mail is successfully sent to that address though it wasnt your intention ... unless of course your intention was spamming ;) ... So, it is important to first check for accuracy of your send list addresses ... and then you can check for a successful sending of the mail to the correct address using the code below which is given in the synopsis of the module you mentioned.

eval { $sender->send($email) };
die "Error sending email: $@" if $@;
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The one another way is, you can specify the reply-to parameter in the argument. So if the server could not find the mail id, it will return the error message (Undeliverable or bounce mail) to your mail which has been specified in the argument. So you can get to know whether the mail id is existing or not. The bounce mail will come for some other reason also like attached file size exceeded and so on. Please ensure, there is no problem in the mail in your mail server.