Don't block emails if Sendingblue SMTP is not configured for transactional emails.

[yutv]

Currently when the module is installed you can't longer use the hosting provided SMTP server, you either forced to use Sendinblue one or emails will be BLOCKED by the module. It is very disappointing. Please fix that ASAP.

[kestraly]

From memory, if you have no intention of using the transactional feature, you can delete the di.xml file and this will allow another module to use SMTP etc for sending