• Open Thunderbird.
• Click the Menu button (three horizontal lines) and select Account Settings.
• Choose your email account from the list on the left.
• Under Server Settings, check your Username:
  • If it’s "myusername," change it to "myusername@meganet.net" for the Incoming server.
• Scroll down to Outgoing Server (SMTP) and click Edit.
• Under Username, ensure it reads "myusername@meganet.net" (append "@meganet.net" if it’s missing).
• Ensure your Outgoing SMTP server is set to: smtp.meganet.net.
• Click OK to save your changes.