All was working, no changes were made and now all users who use outlook get the following message when sending email:
Sending' reported error (0x80042109) : 'Outlook cannot connect to your outgoing (SMTP) e-mail server. If you continue to receive this message, contact your server administrator or Internet service provider (ISP).'

Receiving works fine but can't send. As stated, I know all the setting are correct because they were working yesterday and this started happening with all users using Outlook. Any help would be appreciated.