Redmine can accept e-mails sent to it through a rake task (client pull) or through a web service (server push). Troubleshooting, in this case, can apply to configuration problems and runtime problems.
To troubleshoot configuration problems, first make sure that your configuration works by testing it manually from the console prior to configuring cron job or scheduled tasks. Scheduled tasks and cron jobs need to execute proper environment (production) and perform as expected.
An example problem would be, as follows:
rake redmine:email:receive_imap RAILS_ENV="production" host=demo.redminegit.com username=redmine.demo password=redmine rake aborted! Net::IMAP::NoResponseError: Authentication failed.
It is clear ...