Thanks for the heads up! It is true that memory consumption on the queue is a concern. I do however still think that using celery is a viable option for email sending. I've in the past used django-mailer by James Tauber, which is basically the same as using this app with ghettoq as the celery backend. While I agree that RabbitMQ may cause problems, and that a well configured MTA is a good and viable solution, I still think that Celery offers some advantages to that approach, especially if someone is already using Celery in their project. Celery offers a wide variety of backends, rate limiting, and the ability to scale by using workers on several machines. So I still think that having a good and easily installable django app for this problem is a good thing, but I definitely agree with you that correctly configuring a queue and scaling it is a big task, and that most people should probably stick with exim or postfix like you said.
Also, I thought I had done some good searching to make sure I wasn't duplicating effort but appear to have failed. I even named my project the same as the repo to which you linked. I'll have to contact schinckel and apologize.