Forbidden: 403 Forbidden (error code: 50007): Cannot send messages to this user
Sentry Issue: [BOT-13C](https://sentry.io/organizations/python-discord/issues/2453738315/?referrer=github_integration)

```
Forbidden: 403 Forbidden (error code: 50007): Cannot send messages to this user
(2 additional frame(s) were not displayed)
...
  File "bot/utils/lock.py", line 108, in wrapper
    log.debug(
  File "bot/utils/lock.py", line 108, in wrapper
    log.debug(
  File "bot/exts/help_channels/_cog.py", line 583, in notify_session_participants
    await message.author.send(embed=embed)
  File "discord/abc.py", line 935, in send
    data = await state.http.send_message(channel.id, content, tts=tts, embed=embed,
  File "discord/http.py", line 241, in request
    raise Forbidden(r, data)

Unhandled exception in on_message.
```

This is caused when a user turns on help dms, but has dms closed.
We should catch this error and deal with it
diff --git a/bot/exts/help_channels/_cog.py b/bot/exts/help_channels/_cog.py
index 7fb72d7e..a9b84758 100644
--- a/bot/exts/help_channels/_cog.py
+++ b/bot/exts/help_channels/_cog.py
@@ -12,6 +12,7 @@ from discord.ext import commands
 
 from bot import constants
 from bot.bot import Bot
+from bot.constants import Channels, RedirectOutput
 from bot.exts.help_channels import _caches, _channel, _message, _name, _stats
 from bot.utils import channel as channel_utils, lock, scheduling
 
@@ -580,7 +581,22 @@ class HelpChannels(commands.Cog):
                 timestamp=message.created_at
             )
             embed.add_field(name="Conversation", value=f"[Jump to message]({message.jump_url})")
-            await message.author.send(embed=embed)
+
+            try:
+                await message.author.send(embed=embed)
+            except discord.Forbidden:
+                log.trace(
+                    f"Failed to send helpdm message to {message.author.id}. DMs Closed/Blocked. "
+                    "Removing user from helpdm."
+                )
+                bot_commands_channel = self.bot.get_channel(Channels.bot_commands)
+                await _caches.help_dm.delete(message.author.id)
+                await bot_commands_channel.send(
+                    f"{message.author.mention} {constants.Emojis.cross_mark} "
+                    "To receive updates on help channels you're active in, enable your DMs.",
+                    delete_after=RedirectOutput.delete_after
+                )
+                return
 
             await _caches.session_participants.set(
                 message.channel.id,
['bot/exts/help_channels/_cog.py']