I have a file in the root of my project called:

backup/gmail/getmail/oldmail-imap.gmail.com-993-a@b.c-[Gmail].All Mail

This is a typical Getmail log file / config file.

When I add this file to gitignore, it will create the following entry in my repository's gitignore file:

oldmail-imap.gmail.com-993-a@b.c-[Gmail].All Mail

This does not stop git or Sourcetree from detecting the file as new.

Please see the screenshot attached. I've censored the email address. Let me know if I forgot to include vital information.