Solve Shopware Problem

Hy there. We have a Shopware Online Shop at a 1&1 Cloud Server but now it throws errors. We need to get the side runnnin... Actuall we get this failure -> Class Zend_Mail_Transport_Mail does not exist and could not be loaded in engine/Library/Enlight/[login to view URL] on line 158 Stack trace: #0 engine/Library/Enlight/[login to view URL](180): Enlight_Class::getClassName('Zend_Mail_Trans...') #1 engine/Shopware/Components/DependencyInjection/Bridge/[login to view URL](83): Enlight_Class::Instance('Zend_Mail_Trans...') #2 var/cache/production_201904021344/proxies/[login to view URL](1136): Shopware\Components\DependencyInjection\Bridge\MailTransport->factory(Object(Enlight_Loader), Object(Shopware_Components_Config), Array) #3 vendor/symfony/dependency-injection/[login to view URL](306): ShopwareProduction477d8b6ddd716d9ab10d06cfa5b1ae3267f9e278ProjectContainer->getMailTransportService() #4 engine/Shopware/Components/DependencyInjection/[login to view URL](204): Symfony\Component\DependencyInjection\Container->get('MailTransport', 2) #5 engine/Shopware/Components/DependencyInjection/[login to view URL](156): Shopware\Components\DependencyInjection\Container->doLoad('mailtransport') #6 engine/Shopware/Components/DependencyInjection/Bridge/[login to view URL](41): Shopware\Components\DependencyInjection\Container->load('mailtransport') #7 var/cache/production_201904021344/proxies/[login to view URL](4267): Shopware\Components\DependencyInjection\Bridge\TemplateMail->factory(Object(ShopwareProduction477d8b6ddd716d9ab10d06cfa5b1ae3267f9e278ProjectContainer)) #8 vendor/symfony/dependency-injection/[login to view URL](306): ShopwareProduction477d8b6ddd716d9ab10d06cfa5b1ae3267f9e278ProjectContainer->getTemplatemailService() #9 engine/Shopware/Components/DependencyInjection/[login to view URL](204): Symfony\Component\DependencyInjection\Container->get('templatemail', 1) #10 engine/Shopware/Components/DependencyInjection/[login to view URL](138): Shopware\Components\DependencyInjection\Container->doLoad('templatemail', 1) #11 engine/Shopware/Models/Shop/[login to view URL](722): Shopware\Components\DependencyInjection\Container->get('templatemail') #12 engine/Shopware/Controllers/Backend/[login to view URL](97): Shopware\Models\Shop\Shop->registerResources() #13 engine/Library/Enlight/Controller/[login to view URL](192): Shopware_Controllers_Backend_Theme->previewAction() #14 engine/Library/Enlight/Controller/Dispatcher/[login to view URL](563): Enlight_Controller_Action->dispatch('previewAction') #15 engine/Library/Enlight/Controller/[login to view URL](222): Enlight_Controller_Dispatcher_Default->dispatch(Object(Enlight_Controller_Request_RequestHttp), Object(Enlight_Controller_Response_ResponseHttp)) #16 engine/Shopware/[login to view URL](202): Enlight_Controller_Front->dispatch() #17 vendor/symfony/http-kernel/HttpCache/[login to view URL](102): Shopware\Kernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #18 vendor/symfony/http-kernel/HttpCache/[login to view URL](448): Symfony\Component\HttpKernel\HttpCache\SubRequestHandler::handle(Object(Shopware\Kernel), Object(Symfony\Component\HttpFoundation\Request), 1, true) #19 engine/Shopware/Components/HttpCache/[login to view URL](260): Symfony\Component\HttpKernel\HttpCache\HttpCache->forward(Object(Symfony\Component\HttpFoundation\Request), true, NULL) #20 vendor/symfony/http-kernel/HttpCache/[login to view URL](238): Shopware\Components\HttpCache\AppCache->forward(Object(Symfony\Component\HttpFoundation\Request), true) #21 engine/Shopware/Components/HttpCache/[login to view URL](105): Symfony\Component\HttpKernel\HttpCache\HttpCache->pass(Object(Symfony\Component\HttpFoundation\Request), true) #22 [login to view URL](122): Shopware\Components\HttpCache\AppCache->handle(Object(Symfony\Component\HttpFoundation\Request)) #23 {main}