Newsletter content aggregation I'm using the Simplenews module for creating newsletter and I would like to know if it's possible to aggregate different newsletter content into only one for the same subscriber.
For example, one person subscribes to 3 different newsletters on the same website and receives only one newsletter containing the 3 content of those three newsletters.
No, you can't do that with the current version of simplenews.

Some alternatives: 


Use Mailchimp integration and create segments, groups, then use conditional merge tags (http://kb.mailchimp.com/article/all-the-merge-tags-cheatsheet#Conditional) 
You could hack the simplenews module, but that is more shaky... Using the simplenews scheduler and the simplenews content selection module you could patch up a solution. 
The newsletter module might be the best platform to do this as they are active and you might find people who want to collaborate. Also the architecture is more generic.


For the moment I will use #1, but in the future I will probably have to implement a neater solution with #3.