Your SMTP provider is probably blocking the connection, did you review that?
If you are using Gmail, that guide will probably help you debug the issue. If you are using any other SMTP provider, please ensure the configuration is the proper one and that the provider doesn't block that connection. You can also use other SMTP providers like Sendgrid to ensure the SMTP are being sent properly.
If you have more questions, I also suggest you ask in the official forums of the application to know how to debug that.