diff --git a/readthedocs/config/exceptions.py b/readthedocs/config/exceptions.py
index ea76ce0cbcf..637ffd71cf7 100644
--- a/readthedocs/config/exceptions.py
+++ b/readthedocs/config/exceptions.py
@@ -11,7 +11,6 @@ class ConfigError(BuildUserError):
         "config:python:use-system-site-packages-removed"
     )
     INVALID_VERSION = "config:base:invalid-version"
-    GENERIC_INVALID_CONFIG_KEY = "config:key:generic-invalid-config-key"
     NOT_BUILD_TOOLS_OR_COMMANDS = "config:build:missing-build-tools-commands"
     BUILD_JOBS_AND_COMMANDS = "config:build:jobs-and-commands"
     APT_INVALID_PACKAGE_NAME_PREFIX = "config:apt:invalid-package-name-prefix"
diff --git a/readthedocs/config/notifications.py b/readthedocs/config/notifications.py
index f073dd1c6a2..b6f744c6af0 100644
--- a/readthedocs/config/notifications.py
+++ b/readthedocs/config/notifications.py
@@ -29,7 +29,8 @@
         body=_(
             textwrap.dedent(
                 """
-            No default configuration file found at repository's root.
+            The required <code>readthedocs.yaml</code> configuration file was not found at repository's root.
+            Learn how to use this file in our <a href="https://docs.readthedocs.io/en/stable/config-file/index.html">configuration file tutorial</a>.
             """
             ).strip(),
         ),
@@ -66,8 +67,8 @@
             textwrap.dedent(
                 """
             The configuration key <code>python.system_packages</code> has been deprecated and removed.
-            Refer to https://blog.readthedocs.com/drop-support-system-packages/ to read more
-            about this change and how to upgrade your config file."
+            <a href="https://blog.readthedocs.com/drop-support-system-packages/">Read our blog post</a>
+            to learn more about this change and how to upgrade your configuration file."
             """
             ).strip(),
         ),
@@ -80,8 +81,8 @@
             textwrap.dedent(
                 """
             The configuration key <code>python.use_system_site_packages</code> has been deprecated and removed.
-            Refer to https://blog.readthedocs.com/drop-support-system-packages/ to read more
-            about this change and how to upgrade your config file."
+            <a href="https://blog.readthedocs.com/drop-support-system-packages/">Read our blog post</a>
+            to learn more about this change and how to upgrade your configuration file."
             """
             ).strip(),
         ),
@@ -99,29 +100,13 @@
         ),
         type=ERROR,
     ),
-    Message(
-        id=ConfigError.GENERIC_INVALID_CONFIG_KEY,
-        header=_("Invalid configuration option"),
-        body=_(
-            textwrap.dedent(
-                """
-            Invalid configuration option: <code>{{key}}</code>.
-
-            Read the Docs configuration file: <code>{{source_file}}</code>.
-
-            <code>{{error_message}}</code>
-            """
-            ).strip(),
-        ),
-        type=ERROR,
-    ),
     Message(
         id=ConfigError.NOT_BUILD_TOOLS_OR_COMMANDS,
-        header=_("Invalid configuration option: <code>build</code>"),
+        header=_("Missing configuration option"),
         body=_(
             textwrap.dedent(
                 """
-            At least one item should be provided in "tools" or "commands".
+            At least one of the following configuration options is required: <code>build.tools</code> or <code>build.commands</code>.
             """
             ).strip(),
         ),
@@ -169,7 +154,8 @@
         body=_(
             textwrap.dedent(
                 """
-            You need to install your project with pip to use <code>extra_requirements</code>.
+            You need to install your project with <code>python.install.method: pip</code>
+            to use <code>python.install.extra_requirements</code>.
             """
             ).strip(),
         ),
@@ -177,11 +163,12 @@
     ),
     Message(
         id=ConfigError.PIP_PATH_OR_REQUIREMENT_REQUIRED,
-        header=_("Invalid configuration key"),
+        header=_("Missing configuration key"),
         body=_(
             textwrap.dedent(
                 """
-            <code>path</code> or <code>requirements</code> key is required for <code>python.install</code>.
+                When using <code>python.install</code>,
+                one of the following keys are required: <code>python.install.path</code> or <code>python.install.requirements</code>.
             """
             ).strip(),
         ),
@@ -205,7 +192,7 @@
         body=_(
             textwrap.dedent(
                 """
-            You can not have <code>exclude</code> and <code>include</code> submodules at the same time.
+            You can not have <code>submodules.exclude</code> and <code>submodules.include</code> at the same time.
             """
             ).strip(),
         ),
@@ -230,6 +217,7 @@
             textwrap.dedent(
                 """
             Error while parsing <code>{{filename}}</code>.
+            Make sure your configuration file doesn't have any errors.
 
             {{error_message}}
             """
@@ -261,7 +249,8 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected one of (0, 1, true, false), got <code>{{value}}</code>.
+            Expected one of <code>[0, 1, true, false]</code>, got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
+            Make sure the type of the value is not a string.
             """
             ).strip(),
         ),
@@ -274,7 +263,9 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected one of ({{choices}}), got <code>{{value}}</code>.
+            Expected one of ({{choices}}), got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
+            Double check the type of the value.
+            A string may be required (e.g. <code>"3.10"</code> insted of <code>3.10</code>)
             """
             ).strip(),
         ),
@@ -287,7 +278,7 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected a dictionary, got <code>{{value}}</code>.
+            Expected a dictionary, got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
             """
             ).strip(),
         ),
@@ -326,7 +317,7 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected a string, got <code>{{value}}</code>.
+            Expected a string, got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
             """
             ).strip(),
         ),
@@ -339,7 +330,7 @@
             textwrap.dedent(
                 """
             Config validation error in <code>{{key}}</code>.
-            Expected a list, got <code>{{value}}</code>.
+            Expected a list, got type <code>{{value|to_class_name}}</code> (<code>{{value}}</code>).
             """
             ).strip(),
         ),
diff --git a/readthedocs/doc_builder/backends/mkdocs.py b/readthedocs/doc_builder/backends/mkdocs.py
index 570b1a93404..cd4a256e0b1 100644
--- a/readthedocs/doc_builder/backends/mkdocs.py
+++ b/readthedocs/doc_builder/backends/mkdocs.py
@@ -168,9 +168,10 @@ def append_conf(self):
                 value = []
             if not isinstance(value, list):
                 raise MkDocsYAMLParseError(
-                    MkDocsYAMLParseError.INVALID_EXTRA_CONFIG.format(
-                        config=config,
-                    ),
+                    message_id=MkDocsYAMLParseError.INVALID_EXTRA_CONFIG,
+                    format_values={
+                        "extra_config": config,
+                    },
                 )
             # Add the static file only if isn't already in the list.
             value.extend([extra for extra in extras if extra not in value])
diff --git a/readthedocs/doc_builder/backends/sphinx.py b/readthedocs/doc_builder/backends/sphinx.py
index b4d2ddc6988..7997e018b2f 100644
--- a/readthedocs/doc_builder/backends/sphinx.py
+++ b/readthedocs/doc_builder/backends/sphinx.py
@@ -258,7 +258,10 @@ def append_conf(self):
 
         if not os.path.exists(self.config_file):
             raise UserFileNotFound(
-                UserFileNotFound.FILE_NOT_FOUND.format(self.config_file)
+                message_id=UserFileNotFound.FILE_NOT_FOUND,
+                format_values={
+                    "filename": os.path.relpath(self.config_file, self.project_path),
+                },
             )
 
         # Allow symlinks, but only the ones that resolve inside the base directory.
diff --git a/readthedocs/doc_builder/exceptions.py b/readthedocs/doc_builder/exceptions.py
index b13e9ba2b74..0e67422a6b4 100644
--- a/readthedocs/doc_builder/exceptions.py
+++ b/readthedocs/doc_builder/exceptions.py
@@ -35,7 +35,6 @@ class BuildAppError(BuildBaseException):
 class BuildUserError(BuildBaseException):
     GENERIC = "build:user:generic"
     SKIPPED_EXIT_CODE_183 = "build:user:exit-code-183"
-    MAX_CONCURRENCY = "build:user:max-concurrency"
 
     BUILD_COMMANDS_WITHOUT_OUTPUT = "build:user:output:no-html"
     BUILD_OUTPUT_IS_NOT_A_DIRECTORY = "build:user:output:is-no-a-directory"
diff --git a/readthedocs/doc_builder/python_environments.py b/readthedocs/doc_builder/python_environments.py
index c11c0f10553..4af234e64b3 100644
--- a/readthedocs/doc_builder/python_environments.py
+++ b/readthedocs/doc_builder/python_environments.py
@@ -291,9 +291,10 @@ def _append_core_requirements(self):
             )
             if not inputfile:
                 raise UserFileNotFound(
-                    UserFileNotFound.FILE_NOT_FOUND.format(
-                        self.config.conda.environment
-                    )
+                    message_id=UserFileNotFound.FILE_NOT_FOUND,
+                    format_values={
+                        "filename": self.config.conda.environment,
+                    },
                 )
             environment = parse_yaml(inputfile)
         except IOError:
@@ -334,9 +335,10 @@ def _append_core_requirements(self):
                 )
                 if not outputfile:
                     raise UserFileNotFound(
-                        UserFileNotFound.FILE_NOT_FOUND.format(
-                            self.config.conda.environment
-                        )
+                        message_id=UserFileNotFound.FILE_NOT_FOUND,
+                        format_values={
+                            "filename": self.config.conda.environment,
+                        },
                     )
                 yaml.safe_dump(environment, outputfile)
             except IOError:
diff --git a/readthedocs/notifications/messages.py b/readthedocs/notifications/messages.py
index 4684f566ae1..28c43b453ff 100644
--- a/readthedocs/notifications/messages.py
+++ b/readthedocs/notifications/messages.py
@@ -58,18 +58,24 @@ def get_display_icon_classes(self):
 
         return " ".join(classes)
 
+    def _prepend_template_prefix(self, template):
+        """
+        Prepend Django {% load %} template tag.
+
+        This is required to render the notifications with custom filters/tags.
+        """
+        prefix = "{% load notifications_filters %}"
+        return prefix + template
+
     def get_rendered_header(self):
-        template = Template(self.header)
+        template = Template(self._prepend_template_prefix(self.header))
         return template.render(context=Context(self.format_values))
 
     def get_rendered_body(self):
-        template = Template(self.body)
+        template = Template(self._prepend_template_prefix(self.body))
         return template.render(context=Context(self.format_values))
 
 
-# TODO: review the copy of these notifications/messages on PR review and adapt them.
-# Most of them are copied from what we had in `readthedocs.doc_builder.exceptions`
-# and slightly adapted to have a header and a better body.
 BUILD_MESSAGES = [
     Message(
         id=BuildAppError.GENERIC_WITH_BUILD_ID,
@@ -122,11 +128,12 @@ def get_rendered_body(self):
         body=_(
             textwrap.dedent(
                 """
-            Concurrency limit reached ({{limit}}), retrying in 5 minutes.
+            Your project, organization, or user has reached its maximum number of concurrent builds allowed ({{limit}}).
+            This build will automatically retry in 5 minutes.
             """
             ).strip(),
         ),
-        type=INFO,
+        type=ERROR,
     ),
     Message(
         id=BuildCancelled.CANCELLED_BY_USER,
@@ -142,7 +149,7 @@ def get_rendered_body(self):
     ),
     Message(
         id=BuildUserError.SKIPPED_EXIT_CODE_183,
-        header=_("Build skipped manually."),
+        header=_("Build skipped."),
         body=_(
             textwrap.dedent(
                 """
@@ -155,11 +162,12 @@ def get_rendered_body(self):
     ),
     Message(
         id=BuildUserError.BUILD_TIME_OUT,
-        header=_("Build exited due to time out."),
+        header=_("Build terminated due to time out."),
         body=_(
             textwrap.dedent(
                 """
-            Build exited due to time out.
+            The build was terminated due to time out.
+            Read more about <a href="https://docs.readthedocs.io/en/stable/builds.html#build-resources">time and memory limits in our documentation</a>.
             """
             ).strip(),
         ),
@@ -167,11 +175,12 @@ def get_rendered_body(self):
     ),
     Message(
         id=BuildUserError.BUILD_EXCESSIVE_MEMORY,
-        header=_("Build exited due to excessive memory consumption."),
+        header=_("Build terminated due to excessive memory consumption."),
         body=_(
             textwrap.dedent(
                 """
-            Build exited due to excessive memory consumption.
+            This build was terminated due to excessive memory consumption.
+            Read more about <a href="https://docs.readthedocs.io/en/stable/builds.html#build-resources">time and memory limits in our documentation</a>.
             """
             ).strip(),
         ),
@@ -179,11 +188,11 @@ def get_rendered_body(self):
     ),
     Message(
         id=BuildAppError.BUILD_DOCKER_UNKNOWN_ERROR,
-        header=_("Build exited due to unknown error."),
+        header=_("Build terminated due to unknown error."),
         body=_(
             textwrap.dedent(
                 """
-            Build exited due to unknown error: {{message}}
+            This build was terminated due to unknown error: {{message}}
             """
             ).strip(),
         ),
@@ -203,19 +212,6 @@ def get_rendered_body(self):
         ),
         type=ERROR,
     ),
-    Message(
-        id=BuildUserError.MAX_CONCURRENCY,
-        header=_("Concurrency limit reached"),
-        body=_(
-            textwrap.dedent(
-                """
-            Your project, organization, or user is currently building the maximum concurrency builds allowed ({{limit}}).
-            It will automatically retry in 5 minutes.
-            """
-            ).strip(),
-        ),
-        type=WARNING,
-    ),
     Message(
         id=BuildUserError.BUILD_COMMANDS_WITHOUT_OUTPUT,
         header=_("No HTML content found"),
@@ -235,6 +231,7 @@ def get_rendered_body(self):
             textwrap.dedent(
                 """
             Build output directory for format "{{artifact_type}}" is not a directory.
+            Make sure you created this directory properly when running <code>build.commands</code>.
             """
             ).strip(),
         ),
@@ -273,7 +270,7 @@ def get_rendered_body(self):
         body=_(
             textwrap.dedent(
                 """
-            Your documentation did not generate an 'index.html' at its root directory.
+            Your documentation did not generate an <code>index.html</code> at its root directory.
             This is required for documentation serving at the root URL for this version.
             """
             ).strip(),
@@ -286,9 +283,9 @@ def get_rendered_body(self):
         body=_(
             textwrap.dedent(
                 """
-            Some files were detected in an unsupported output path, '_build/html'.
+            Some files were detected in an unsupported output path: <code>_build/html</code>.
             Ensure your project is configured to use the output path
-            '$READTHEDOCS_OUTPUT/html' instead.
+            <code>$READTHEDOCS_OUTPUT/html</code> instead.
             """
             ).strip(),
         ),
@@ -302,7 +299,7 @@ def get_rendered_body(self):
                 """
             The configuration file required to build documentation is missing from your project.
             Add a configuration file to your project to make it build successfully.
-            Read more at https://docs.readthedocs.io/en/stable/config-file/v2.html
+            Read more in our <a href="https://docs.readthedocs.io/en/stable/config-file/v2.html">configuration file documentation</a>.
             """
             ).strip(),
         ),
@@ -314,9 +311,9 @@ def get_rendered_body(self):
         body=_(
             textwrap.dedent(
                 """
-            The configuration key "build.image" is deprecated.
-            Use "build.os" instead to continue building your project.
-            Read more at https://docs.readthedocs.io/en/stable/config-file/v2.html#build-os
+            The configuration key <code>build.image</code> is deprecated.
+            Use <code>build.os</code> instead to continue building your project.
+            Read more in our <a href="https://docs.readthedocs.io/en/stable/config-file/v2.html#build-os">configuration file documentation</a>.
             """
             ).strip(),
         ),
@@ -328,13 +325,14 @@ def get_rendered_body(self):
         body=_(
             textwrap.dedent(
                 """
-            The configuration key "build.os" is required to build your documentation.
-            Read more at https://docs.readthedocs.io/en/stable/config-file/v2.html#build-os
+            The configuration key <code>build.os</code> is required to build your documentation.
+            Read more in our <a href="https://docs.readthedocs.io/en/stable/config-file/v2.html#build-os">configuration file documentation</a>.
             """
             ).strip(),
         ),
         type=ERROR,
     ),
+    # TODO: consider exposing the name of the file exceeding the size limit.
     Message(
         id=BuildUserError.FILE_TOO_LARGE,
         header=_("There is at least one file that exceeds the size limit"),
@@ -355,6 +353,7 @@ def get_rendered_body(self):
             textwrap.dedent(
                 f"""
              PDF file was not generated/found in "{BUILD_COMMANDS_OUTPUT_PATH_HTML}/pdf" output directory.
+             Make sure the PDF file is saved in this directory.
              """
             ).strip(),
         ),
@@ -366,7 +365,7 @@ def get_rendered_body(self):
         body=_(
             textwrap.dedent(
                 """
-            <strong>The <code>"build.commands"</code> feature is in beta, and could have backwards incompatible changes while in beta.</strong>
+            <strong>The <code>build.commands</code> feature is in beta, and could have backwards incompatible changes while in beta.</strong>
             Read more at <a href=""https://docs.readthedocs.io/page/build-customization.html#override-the-build-process">our documentation</a> to find out its limitations and potential issues.
             """
             ).strip(),
@@ -379,7 +378,7 @@ def get_rendered_body(self):
         body=_(
             textwrap.dedent(
                 """
-            No TeX files were found.
+            Read the Docs could not generate a PDF file because the intermediate step generating the TeX file failed.
             """
             ).strip(),
         ),
@@ -402,11 +401,11 @@ def get_rendered_body(self):
     ),
     Message(
         id=MkDocsYAMLParseError.INVALID_DOCS_DIR_CONFIG,
-        header=_(""),
+        header=_("MkDocs <code>docs_dir</code> configuration option is invalid"),
         body=_(
             textwrap.dedent(
                 """
-            The "docs_dir" config from your MkDocs YAML config file has to be a
+            The <code>docs_dir</code> option from your <code>mkdocs.yml</code> configuration file has to be a
             string with relative or absolute path.
             """
             ).strip(),
@@ -415,10 +414,12 @@ def get_rendered_body(self):
     ),
     Message(
         id=MkDocsYAMLParseError.INVALID_DOCS_DIR_PATH,
-        header=_(""),
+        header=_("MkDocs <code>docs_dir</code> path not found"),
         body=_(
             textwrap.dedent(
                 """
+                The path specified by <code>docs_dir</code> in the <code>mkdocs.yml</code> file does not exist.
+                Make sure this path is correct.
             """
             ).strip(),
         ),
@@ -426,11 +427,13 @@ def get_rendered_body(self):
     ),
     Message(
         id=MkDocsYAMLParseError.INVALID_EXTRA_CONFIG,
-        header=_(""),
+        header=_(
+            "MkDocs <code>{{extra_config}}</code> configuration option is invalid"
+        ),
         body=_(
             textwrap.dedent(
                 """
-            The "{{config}}" config from your MkDocs YAML config file has to be a
+            The <code>{{extra_config}}</code> option from your <code>mkdocs.yml</code> configuration file has to be a
             list of relative paths.
             """
             ).strip(),
@@ -439,11 +442,11 @@ def get_rendered_body(self):
     ),
     Message(
         id=MkDocsYAMLParseError.EMPTY_CONFIG,
-        header=_(""),
+        header=_("MkDocs configuration file is empty"),
         body=_(
             textwrap.dedent(
                 """
-            Please make sure the MkDocs YAML configuration file is not empty.
+            Please make sure the <code>mkdocs.yml</code> configuration file is not empty.
             """
             ).strip(),
         ),
@@ -451,12 +454,13 @@ def get_rendered_body(self):
     ),
     Message(
         id=MkDocsYAMLParseError.NOT_FOUND,
-        header=_(""),
+        header=_("MkDocs configuration file not found"),
         body=_(
             textwrap.dedent(
                 """
-            A configuration file was not found.
-            Make sure you have a "mkdocs.yml" file in your repository.
+            The configuration file for MkDocs was not found.
+            Make sure the <code>mkdocs.configuration</code> option is correct,
+            and you have the <code>mkdocs.yml</code> in that location.
             """
             ).strip(),
         ),
@@ -464,12 +468,12 @@ def get_rendered_body(self):
     ),
     Message(
         id=MkDocsYAMLParseError.CONFIG_NOT_DICT,
-        header=_(""),
+        header=_("Unknown error when loading your MkDocs configuration file"),
         body=_(
             textwrap.dedent(
                 """
-            Your MkDocs YAML config file is incorrect.
-            Please follow the user guide https://www.mkdocs.org/user-guide/configuration/
+            Your <code>mkdocs.yml</code> configuration file is incorrect.
+            Please follow the <a href="https://www.mkdocs.org/user-guide/configuration/">official user guide</a>
             to configure the file properly.
             """
             ).strip(),
diff --git a/readthedocs/notifications/templatetags/notifications_filters.py b/readthedocs/notifications/templatetags/notifications_filters.py
new file mode 100644
index 00000000000..96ad0101fc3
--- /dev/null
+++ b/readthedocs/notifications/templatetags/notifications_filters.py
@@ -0,0 +1,9 @@
+from django import template
+
+register = template.Library()
+
+
+@register.filter
+def to_class_name(value):
+    """Output the name of the class for the given object."""
+    return value.__class__.__name__
diff --git a/readthedocs/projects/tasks/builds.py b/readthedocs/projects/tasks/builds.py
index ed7c15b668c..69570d2994a 100644
--- a/readthedocs/projects/tasks/builds.py
+++ b/readthedocs/projects/tasks/builds.py
@@ -295,18 +295,19 @@ class UpdateDocsTask(SyncRepositoryMixin, Task):
         RepositoryError,
         MkDocsYAMLParseError,
         ProjectConfigurationError,
+        BuildMaxConcurrencyError,
     )
 
     # Do not send notifications on failure builds for these exceptions.
     exceptions_without_notifications = (
         BuildCancelled.CANCELLED_BY_USER,
-        BuildUserError.MAX_CONCURRENCY,
         BuildUserError.SKIPPED_EXIT_CODE_183,
         BuildAppError.BUILDS_DISABLED,
+        BuildMaxConcurrencyError.LIMIT_REACHED,
     )
 
     # Do not send external build status on failure builds for these exceptions.
-    exceptions_without_external_build_status = (BuildUserError.MAX_CONCURRENCY,)
+    exceptions_without_external_build_status = (BuildMaxConcurrencyError.LIMIT_REACHED,)
 
     acks_late = True
     track_started = True