Github user olegz commented on the issue:
https://github.com/apache/nifi/pull/710
One advise though is that there are additional JavaMail properties that one
may need to provide to accomodate specific servers. For example in Gmail you
need to specify
```mail.pop3.socketFactory.class=javax.net.ssl.SSLSocketFactory``` and possibly
few more (depending on your server settings). Those should be set as Dynamic
properties since there is no common set. One property you should definitely set
to get more info as to what is happening is ```mail.debug=true```. That will
spit out all kinds of protocol messages which could explain what is going on.
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at [email protected] or file a JIRA ticket
with INFRA.
---
