I can provide clarification about sending emails.
If you're trying to send your transactions within your email account, you’ll need to check the email provider if there are any ongoing issues.
However, if you’re sending the mass emails through QuickBooks Online, can you please provide a screenshot so I can check? This way, I can look into this further and verify why you can only save it as a draft.
Any additional details are greatly appreciated.
In case you need help designing the invoice you'll send to your customer, you can refer to this link: Customize your invoice emails.
If you have follow-up questions, feel free to drop it in the comment section below.
