Why laravel queue attempting same job multiple time if email address is valid?

I have to send mail through laravel application, first I used simple laravel Mail function, but it was taking lot of time when I was sending 10-15 emails, So I implement Queue. Also put command - php artisan queue:work - on server.

Issue is sometime it executes all job properly and sometime all jobs will fail, even if I have added correct To-email address. Also why its trying single job multiple time? why its not sending mail same time when first time it executing job?

via Chebli Mohamed