Added support for development SMTP servers like MailHog

[gumannp]

Description

A property describing a port for a local SMTP server (see MailHog) was added. If the property is omitted, sendmail behaves like it used to.

Motivation and Context

This feature makes it possible to test an application offline and for multiple email addresses without needing to create hundreds of mail accounts.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

[GreenPioneer]

Ill check this out later this week or in the beginning of next. Im at Node interactive conf currently

[GreenPioneer]

I got to review it briefly but i like it. Im gonna do a more in-depth look at the code but regardless i will probably accept within the next couple days