Running case together is failing

I have developed an email service using Spring Boot App. My project structure looks like: MailServiceProject -> src -> main ,test test ->java -> org.company.junit -> A, B, C, D

When I run my test case individually from A,B,C or D folder they ran fine.. But if I ran all the test cases from org.company.junit package, some of my test cases always fail. I notice the pattern that the test cases which actually send email out fails. And throws: java.lang.Exception: GeneralException

Is there any way to get more detailed error or any idea why this behave so weirdly.

TIA.