Hi,
There are a couple of things you could check:
Are you able to send/receive a testmail from Acymailings configuration panel?
Are you able to send/receive a test mail from your newsletter?
Can you send/receive Joomla messages (like forgot pasword and account creation)?
When you need more help, please prvoide us with more information on how you configured your send process and let us know if Joomla and Acymailing use the same mail settings or not.