ADDT´s "Send Email" functions are using the PEAR::Mail interface -- the related PEAR files are located in ADDT´s "include" folder and come with several "drivers" for e.g. SMTP and PHP´s native mail()
If your host´s mail server doesn´t support SMTP, you should leave all fields empty in the "Email Settings" section of ADDT´s "Control Panel" -- except the "Default Sender" that´s always required. However, doing so will pass your emails to PEAR´s mail() driver.
Always worked for me BTW, as my host doesn´t support SMTP as well.