RFC0042 to obsolete Send-MailMessage (#160)

* draft plan to deal with send-mailmessage

* clarify timing about warning

* Address grammar issue

* Add an alternative implementation to address feedback

* Update RFC to reflect work which has been done

* Make it clear that removal is no longer the primary option for 6.3

* replace deprecate with obsolete

* Update 1-Draft/RFCXXXX-Send-MailMessage.md

Co-Authored-By: Joel Sallow (/u/ta11ow) <[email protected]>

* Remove opt-in switch from Send-MailMessage RFC

Per conversation with @TravisEz13 and the @PowerShell/powershell-committee, removing the language around an opt-in switch that breaks existing usage. However, we'll be leaving the obsolescence message until an alternative is decided on.

* Prepare Send-MailMessage RFC for acceptance

Author: TravisEz13

5-Final/RFC0042-Send-MailMessage.md

@@ -0,0 +1,87 @@
+---
+RFC: RFC0042
+Author: Travis Plunk
+Status: Final
+SupercededBy: N/A
+Version: 1.0
+Area: cmdlets
+Comments Due: 4/30/2019
+Plan to implement: No
+---
+
+# Obsoleting `Send-MailMessage`
+
+`Send-MailMessage` does not support many modern protocols leading to the inability to use this with modern secure mail services.
+See [DotNet DE0005](https://github.com/dotnet/platform-compat/blob/master/docs/DE0005.md).
+Since the protocols it uses are no longer considered secure, the cmdlet as is should not be used.
+I recommend that we implement a plan to remove the cmdlet from powershell core and, if needed,
+re-implement as a separate module.
+
+## Motivation
+
+### Primary
+
+The underlying API, [`SmtpClient`](https://docs.microsoft.com/dotnet/api/system.net.mail.smtpclient), doesn't support many modern protocols.
+It is compat-only.
+It's great for one off emails from tools, but doesn't scale to modern requirements of the protocol.
+
+### Secondary
+
+    Most major mail platforms now have REST methods to send mail, which allows `Invoke-RestMethod` to allow sending mail messages.
+
+    * gmail
+      * https://developers.google.com/gmail/api/v1/reference/users/messages/send
+      * https://stackoverflow.com/questions/24460422/how-to-send-a-message-successfully-using-the-new-gmail-rest-api
+    * Office365
+      * https://docs.microsoft.com/en-us/previous-versions/office/office-365-api/api/version-2.0/mail-rest-operations#SendMessages
+
+## Obsoletion  Plan
+
+### Add a warning to 6.2
+
+In a 6.2, we have added an obsolete warning to `Send-MailMessage` that an alternative method should be found.
+
+**Note:** Adding an obsolete warning should not break compatibility in any way.
+
+### If needed, develop an alternative
+
+If needed, develop a new cmdlet based on the DotNet recommended solution of [MailKit](https://github.com/jstedfast/MailKit).
+
+## Alternate Proposals and Considerations
+
+### Remove the cmdlet during 6.3
+
+During the development of 6.3, remove the `Send-MailMessage` cmdlet.
+
+Feedback on this option was negative and the RFC has been updated with then next most reasonable option.
+
+### Community replacement
+
+The community could develop a replacement that can could be incorporated back into PowerShell Core.
+This has the disadvantage of increasing the size of PowerShell Core and delaying the solution.
+
+### Positive confirmation of issue in 6.3
+
+We could add a switch requiring the user to accept the risk of using older **possibly** less secure implementations.
+This switch would be called `-AllowUnsecureConnection` and would be mandatory.
+
+**Note:** The switch name is based on the [DSC Property](https://docs.microsoft.com/en-us/powershell/dsc/managing-nodes/metaconfig#configuration-server-blocks)
+
+However, given the high usage of `Send-MailMessage` in automated scenarios (like scheduled tasks),
+and the plan to work on a `MailKit` based alternative, we'd rather leave the cmdlet working as-is
+for the time being.
+
+### Additional considerations
+
+#### GMail REST API
+
+To use the GMail REST API the following additional items are needed
+
+#### WebSafeBase64
+
+For GMail, a MIME message is required to be encoded in this format.
+https://code.google.com/p/stringencoders/wiki/WebSafeBase64
+
+#### Something to compose the MIME message
+
+For GMail, you have to pass the MIME message.