I had this problem. We used to use old Outlook and with new Outlook we were required to use web email. When sending first email of the day, we were prompted to enter password.

Here is what I ended up doing.

Start Quickbooks as Administrator.

Login as admin.

Change to single user mode.

From Reports, select setup scheduled reports.

Follow the instructions and create one report...you will delete this later so it doesn't matter.

It may warn you that you need to set User Access Control at minimum so do this from Windows. From windows type User Account Control from the start button. Select lowest level and accept the warning.

Now send an invoice and it should not require the password again.

Close company file

Login as normal user.

Select multi user mode.

You should now be able to send invoices without the annoying password requirement. 

You may need to add it once for each user but I don't think so.

This solved it for us.