Wordsmith inbound mail documentation more thoroughly

Summary: See D19973. Fix a couple typos and try to make some sections more clear / less scary.

Test Plan: Read text.

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D19986

src/docs/user/configuration/configuring_inbound_email.diviner

@@ -15,34 +15,37 @@ Phabricator can turn email into comments on the relevant discussion thread.
 **Creating Objects**: You can configure an address like `bugs@yourcompany.com`
 to create new objects (like tasks) when users send email.
 
-In either case, users can interact with objects via `!commands` mail commands
+In either case, users can interact with objects via mail commands to apply a
-to apply a broader set of changes to objects (like adding subscribers, closing
+broader set of changes to objects beyond commenting. (For example, you can use
-tasks, or changing priorities) beyond simply commenting.
+`!close` to close a task or `!priority` to change task priority.)
 
 To configure inbound mail, you will generally:
 
   - Configure some mail domain to submit mail to Phabricator for processing.
-  - For handling replies, set `metamta.reply-handler-domain` in configuration.
+  - For handling replies, set `metamta.reply-handler-domain` in your
+    configuration.
   - For handling email that creates objects, configure inbound addresses in the
     relevant application.
 
 See below for details on each of these steps.
 
 
-Approaches
+Configuration Overview
-==========
+======================
 
-Inbound mail can be extremely difficult to configure correctly. This is doubly
+Usually, the most challenging part of configuring inbound mail is getting mail
-true if you use a local MTA.
+delivered to Phabricator for processing. This step can be made much easier if
+you use a third-party mail service which can submit mail to Phabricator via
+webhooks.
 
-There are a few approaches available:
+Some available approaches for delivering mail to Phabricator are:
 
 | Receive Mail With | Setup | Cost | Notes |
 |--------|-------|------|-------|
 | Mailgun | Easy | Cheap | Recommended |
 | Postmark | Easy | Cheap | Recommended |
 | SendGrid | Easy | Cheap | |
-| Local MTA | Extremely Difficult | Free | Strongly discouraged! |
+| Local MTA | Difficult | Free | Discouraged |
 
 The remainder of this document walks through configuring Phabricator to
 receive mail, and then configuring your chosen transport to deliver mail
@@ -53,18 +56,20 @@ Configuring "Reply" Email
 =========================
 
 By default, Phabricator uses a `noreply@phabricator.example.com` email address
-as the "From" (configurable with `metamta.default-address`) and sets
+as the "From" address when it sends mail. The exact address it uses can be
-"Reply-To" to the user generating the email (e.g., by making a comment), if the
+configured with `metamta.default-address`.
-mail was generated by a user action. This means that users can reply (or
+
-reply-all) to email to discuss changes, but the conversation won't be recorded
+When a user takes an action that generates mail, Phabricator sets the
-in Phabricator and users will not be able to take actions like claiming tasks or
+"Reply-To" addresss for the mail to that user's name and address. This means
-requesting changes to revisions.
+that users can reply to email to discuss changes, but: the conversation won't
+be recorded in Phabricator; and users will not be able to use email commands
+to take actions or make edits.
 
 To change this behavior so that users can interact with objects in Phabricator
 over email, change the configuration key `metamta.reply-handler-domain` to some
 domain you configure according to the instructions below, e.g.
-`phabricator.example.com`. Once you set this key, emails will use a
+`phabricator.example.com`. Once you set this key, email will use a
-'Reply-To' like `T123+273+af310f9220ad@phabricator.example.com`, which -- when
+"Reply-To" like `T123+273+af310f9220ad@phabricator.example.com`, which -- when
 configured correctly, according to the instructions below -- will parse incoming
 email and allow users to interact with Differential revisions, Maniphest tasks,
 etc. over email.
@@ -82,8 +87,8 @@ Configuring "Create" Email
 ==========================
 
 You can set up application email addresses to allow users to create objects via
-email. For example, you could configure `bugs@phabricator.example.com` to creat
+email. For example, you could configure `bugs@phabricator.example.com` to
-a Maniphest task out of any email which is sent to it.
+create a Maniphest task out of any email which is sent to it.
 
 You can find application email settings for each application at:
 
@@ -92,7 +97,7 @@ Applications >
 type=instructions, name="Select an Application" >
 icon=cog, name=Configure}
 
-Not all application support creating objects via email.
+Not all applications support creating objects via email.
 
 In some applications, including Maniphest, you can also configure Herald rules
 with the `[ Content source ]` and/or `[ Receiving email address ]` fields to