docs: add Email section — client setup + Baruwa retirement notice

Replaces the three Outlook 2016 articles (WHMCS 2, 3, 9 — ~62k views)
with one client-agnostic setup guide. Outlook 2016 went end of life in
October 2025, and the two archiving articles documented a feature the
current Outlook doesn't have.

Server settings are taken from the live autoconfig endpoint rather than
the old articles: IMAP 993/SSL, POP3 995/SSL, SMTP 587/STARTTLS, username
is the full address. cPanel settings verified against cpanel01.

Adds a Baruwa retirement notice covering the move to Proxmox Mail Gateway
in November 2026. Deliberately frames this as a platform change rather
than describing our current outbound filtering posture — see the PR
discussion.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

astro.config.mjs

@@ -22,6 +22,7 @@ export default defineConfig({
     '/domains/': '/domains/transferring-a-domain-to-us/',
     '/support/': '/support/remote-support/',
     '/cpanel/': '/cpanel/nameservers/',
+    '/email/': '/email/set-up-your-email-client/',
   },
   vite: {
     resolve: {
@@ -96,6 +97,10 @@ export default defineConfig({
           label: 'Domains',
           items: [{ autogenerate: { directory: 'domains' } }],
         },
+        {
+          label: 'Email',
+          items: [{ autogenerate: { directory: 'email' } }],
+        },
         {
           label: 'Support',
           items: [{ autogenerate: { directory: 'support' } }],