[remomartin]

I've been running into an issue recently in QuickBooks where I get a "Delivery Server Down" or "Unable to send your email" error whenever I try sending invoices or sales forms with PDF attachments to clients.
At first, I thought Intuit's servers were completely down, but after troubleshooting a bit, I realized it often comes down to formatting issues or local setup glitches. Here are a few quick checks that helped me resolve it:

• Check Special Characters: Ensure there are no special characters (
  ! @ # $ % ^ & *
  ) in the invoice description, message field, attachment file name, or custom template.
  
• Verify Email Format: Go to Account and Settings > Company and verify that your company email isn't formatted with prefixes like
  email:name@domain.com
  .
  
• PDF Attachment Settings: Under Sales > Online Delivery, try toggling the "PDF Attached" checkbox off and on, then save and retry sending.
  
• Attachment Size & Type: Make sure the attachment isn't a
  .zip
  file and stays under 25 MB.
  

If anyone else is stuck on this error or needs a detailed walkthrough on checking your Adobe PDF settings and SMTP configurations, you can check out this guide: Resolve QuickBooks Delivery Server Down Error.
Has anyone found other triggers for this specific email delivery bug? Would love to hear what worked for you!