I came across a Drupal 7 site that uses the following modules to send a newsletter to users (6000 users subscribed): Simplenews, Mail system, Mime mail, simplenews rules, variable email, HTML mail, and Rules.
Would using only the Newsletter and Webform modules be sufficient?
If I move to a more minimalist solution, how could I save all the 6000 subscribed users?
I think that with 6000+ emails to send you need to use an external mailer like MailChip or MailUp. Remember that these services have the correct infrastructure to support massive send email and dashboard report.
We have written a module for 1 of our clients that permits to create NewsLetters in Drupal and send it via MailUP for example.
However 7 modules to send an email are not a big number because in Drupal each module exec a single work:
In other systems you have a big module that manages all but not so good like single modules for single works. And in many cases the big module is not compatible with other modules. In Drupal I have found only very few cases where a module is not compatible with other modules.
Have a look at my answer to the question about "How to eMail a file uploaded to a Webform to a sysadmin using the Rules module?".
It explains how to use the Rules module for sending an eMail. To do so, it uses the Mail System and Mime Mail modules ... only!
With some commonly used Rules techniques (like Rules Scheduler, Rules components, etc), it should be pretty forward to make that work for your case also. Possibly you may want to add the Webform Rules modules also to further improve your implementation.
The MailChimp module is very minimalist, giving you a very good ecosystem !
You call sync all your leads (users) to a normal mailchimplist.
Here's a tutorial: How-To Article: MailChimp Module for Drupal.
