Evergreen sends emails as part of several of its processes. If you are working with one of these processes, and want to validate your changes locally, you have several options.
Exim has an easy setup in debian, with the exim configure script. For testing purposes, set the email address to be your own.
For testing with live data, exim makes it easy to rewrite recipients, so you can prevent test emails from being sent to real email addresses.
Look for the "REWRITE CONFIGURATION" section in /etc/exim4/exim4.conf.template
Docs are at : https://www.exim.org/exim-html-current/doc/html/spec_html/ch-address_rewriting.html
Something like this sends all mail to a local address.
##Send all messages to root@localhost *@* root@localhost Tbct
If you have access to your postfix production configuration, you can tweak it for your development environment.
For those running a test server with live data that want to test email without worrying about accidentally emailing real people, one method is to force all email delivery to one local account. A guide to do this in postfix is at https://www.euperia.com/wrote/how-to-configure-postfix-to-deliver-all-mail-to-one-mailbox