For macOS users, if your SMTP server uses Kerberos for authentication and every time you send a message, Postbox prompts for Kerberos authentication you might need to do the following:
- In a Finder Window go to: /Library/Preferences
- Locate a fie that ends in .Kerberos and beings with the domain of your SMTP server (i.e. edu.mit.Kerberos)
- Remove this file
- Restart Postbox