QB Issue Resolution:

You have to change the default Before queueing the transactions as To Send. Once they are in the Queue, it is already “copied” and now you need to work on them one at a time.

I am surprised your QB 2010 even sends email, still. Supposedly, your program no longer has that function. You must be sending through the QB servers, still?

Resolution for Issue 'changing default email for invoicing' available: Yes (Solved).
Source: Intuit Community forum.

changing default email for invoicing: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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