Summary
The Bounce module collects non-delivery reports generated by remote mail servers in response to emails sent from your Drupal site. It parses these non-delivery reports for response codes, scores those codes, and blocks further emails from being sent to email addresses that have passed a score threshold. This helps prevent your site from looking like a spam source by being a good internet citizen and respecting non-delivery responses, such as a notice that a recipient email account no longer exists.
This module is a rewrite of non-Drupal code that itself resulted from some years of experience running a few-thousand-subscriber mailing list covering the sane end of a topic that, unfortunately, tends to trigger spam filters - because there is a large and obnoxious spam-generating industry over at the other, less sane end of the pool. The default settings in Bounce are geared towards helping to maintain good long-term deliverability of mail under that sort of circumstance.
Bounce employs a modular design in which the functionality necessary to analyze and respond to non-delivery reports is split between Connector, Analyst, and Blocker components. Default, working versions of these components are provided, and developers can easily add other implementations through hooks defined in this module.
Alternatives for Drupal 8
Bounce as yet is not ported to Drupal 8. One viable alternative is Inmail.