I deleted that App on my Android device. Nevertheless Notifications continue to be send to my mailbox. Is there a way to stop this?
If you are referring to receiving emails from your tasks then please head to Todoist.com, and under Reminders you will be able to choose No Default Reminder. Also, you should not be receiving reminders unless you have a task with a reminder.
Under the same area, Account, you can also turn off the Daily Digest and Newsletter.