to restart the mailing the mailing, in the mailing manager, stop it, then start it again.
Like i say, there are many possible reasons for the mailing to hang, i just gave a couple examples.
your settings look fine, but that doesn't necessarily mean the server may not time out. sometimes, the server may not get a response from the SMTP server, that may cause the script to hang, as just another example.
That is why it is possible to restart the mailing.