MailSlurper, now with documentation

Another good one is MailCatcher[0] - it includes a nice API and clean ruby gem client.

Brings to mind one of my favorite pieces of Python code:

https://github.com/kennethreitz/inbox.py/blob/master/inbox.p...

A mail server in 64 lines of code.

It doesn't store to a database as Mailslurper does, nor does it have many of other features of Mailslurper.

Mailinator has a Saas option for this (api, private domain, etc).

As does Mailtrap[0] which is apparently used by GitHub and Atlassian among others. (No affiliation, just happened to see their customer list and was somewhat impressed.)

[0] https://mailtrap.io/

I've used MockSMTP (a Mac app) for this purpose before, this looks like a good candidate for shared dev/test/staging environments.