send an email automatically when the due date is reached even when excel is closed

isnt there a way to send email automatically even excel is closed

not that i am aware of

you can however make the macro automatically run when you open excel
just add it to workbook_open event
http://www.ozgrid.com/VBA/auto-run-macros.htm

if you do this then you will also need to ensure you have the workbook every day
or have it on a Task scheduler (this is off topic, as it no longer relates to excel but windows/possibly mac i am not too familiar with mac) to open the excel by itself but then you must have the computer on at the time the task is scheduled

Suggest you google Task Scheduler if you wish to head down that route

If excel isn't open then excel isn't your primary solution.
Find something that is open and use that to open excel at the right time to send the email.
maybe use the Windows Task Scheduler. google it for instructions on your OS.