feat: IMAP Email Channel (#3298)

This change allows the user to configure both IMAP and SMTP for an email inbox. IMAP enables the user to see emails in Chatwoot. And user can use SMTP to reply to an email conversation.

Users can use the default settings to send and receive emails for email inboxes if both IMAP and SMTP are disabled.

Fixes #2520

app/helpers/api/v1/inboxes_helper.rb

@@ -0,0 +1,33 @@
+module Api::V1::InboxesHelper
+  def validate_email_channel(attributes)
+    channel_data = permitted_params(attributes)[:channel]
+
+    validate_imap(channel_data)
+    validate_smtp(channel_data)
+  end
+
+  private
+
+  def validate_imap(channel_data)
+    return unless channel_data.key?('imap_enabled') && channel_data[:imap_enabled]
+
+    Mail.defaults do
+      retriever_method :imap, { address: channel_data[:imap_address],
+                                port: channel_data[:imap_port],
+                                user_name: channel_data[:imap_email],
+                                password: channel_data[:imap_password],
+                                enable_ssl: channel_data[:imap_enable_ssl] }
+    end
+
+    Mail.connection do # rubocop:disable:block
+    end
+  end
+
+  def validate_smtp(channel_data)
+    return unless channel_data.key?('smtp_enabled') && channel_data[:smtp_enabled]
+
+    smtp = Net::SMTP.start(channel_data[:smtp_address], channel_data[:smtp_port], channel_data[:smtp_domain], channel_data[:smtp_email],
+                           channel_data[:smtp_password], :login)
+    smtp.finish unless smtp&.nil?
+  end
+end