I have done all the steps listed below, and none have worked. I am trying to send out invoices. This started this morning. 

Learn how to fix the error “Delivery Server Down” in QuickBooks Online.

The error “Delivery Server Down” is usually related to attachments in your sales or invoice when sending it to a customer. Or, it may depend on how you set up the company email address. Use these steps to fix the error and send your transaction with attachments.

Check your email address format

Check your company and customer-facing email address

Make sure your company email and all customer-facing email fields are complete, have the correct format, and don't have prefixes.

1. Go to Settings ⚙.
2. Select Account and settings, then Company.
3. Select Contact info, then check your Company email and Customer-facing email. Use these examples as a reference on what format to use:
   • Correct: [email address removed]
   • Incorrect: email:[email address removed]

Check your location’s email address

If you use location tracking, check the email address format of the location you used on the sales form. If not, then skip to the next section.

1. Go to Settings ⚙.
2. Select All lists, then Locations.
3. Find the location you used on the invoice.
4. In the ACTION column, select the dropdown, then Edit.
5. Check your email address in the field “This location has a different email address for communicating with customers” and make changes if needed.
6. Select Save.
7. Try to resend your sales form.

Check your invoice format

Open the invoice you tried to send and make sure it doesn’t have special characters (! @ # $ % ^ & *( ) _- = + : ") on the following info:

• Description
• Attachment name 
• Message
• Email address 
• Custom form templates

Check your sales forms email option

Update the attachment setting when emailing sales forms.

1. Go to Settings ⚙.
2. Select Account and settings, then Sales.
3. Select Online delivery, then select or clear the PDF Attached checkbox.
4. Select Save, then Done.
5. Try to resend your sales form.

Check your print and PDF settings

Make sure the file you're attaching isn’t a ZIP file and the size doesn’t exceed 25 MB. If the file name has special characters, remove them.

Check your Adobe Acrobat or Reader settings

Set up the following print options on your Adobe Acrobat or Reader.

• Size: Actual size
• Orientation: Automatic
• Choose paper source by PDF page size: On

Check your browser’s PDF setting

• If you use Google Chrome, refer to their article on how to change default PDF download permissions.
• If you use Firefox, refer to their article on how to set Adobe Reader as the default PDF viewer.

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