I suggest you check again your mail server first. Please notice that our SMTP module is just a tool, your mail server should be able to work itself first.
To test its functions. Please follow this instruction
Then you can ask your host provider about this, they will help you troubleshoot SMTP issues.
If you are using google, you need to do some extra settings, please follow this link
If you did all the things or the host provider confirms everything is working, please let us know, we will check the issue for you.
If you still cannot resolve the issue, you can get help here