If you are using Microsoft Outlook as your mail system and are getting errors saying things along the line of "You Do Not Have Authority To Send From This Account" this is likely to be related to the configuration of the email section of the P11D Organiser.
To check your settings, and correct them if necessary, please follow the steps below:
From the Admin menu, select System Configuration and Setup
You should see a screen similar to the one below.
If your screen is similar to this with information showing in the Email from and Sender name fields, we need to make a few changes, as these are causing the issues.
From the Email system drop down, please select Internet Mail SMTP
This will make the the Email from and Sender name fields editable - we need to delete the data in those two fields.
Once complete, click the OK button and the window will close.
We now need to use Admin>System Configuration and Setup again and re-select Microsoft Outlook from the Email system drop down.
You should now be able to use the Send Test Email button to check that everything is working.