You can go to the Online delivery option to change the format when sending an email, @Venrup PK.
When emails lose formatting when sending emails in QuickBooks Online (QBO), it's usually because they're set to Plain text. To fix this, you'll need to change it to Online invoice delivery.
Here's how:
- Go to the Gear icon, then select Account and Settings.

- Navigate to the Sales tab.
- Locate the Online delivery option, then choose Online invoice.

- Once done, select Save.
This changes the format of the email. Send a sample email to check out the formatting changes.

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To learn how to personalize and add specific info to your sales forms, you can visit this article: Customize invoices, estimates, and sales receipts in QuickBooks Online.
You can always visit to the Community if you have further concerns.