I've been dealing with this situation for about a year when trying to send with one of our email addresses. I've upgraded to the latest Quickbooks, checked the firewall settings, ports, webmail settings, and tried all sorts of "fixes". Our primary email had been a verizon.net email until this issues started and had to switch to using a new email (gmail) for sending out all billing invoices. However, we still need to be able to use the verizon.net email for proposals so that person can communicate with the customer and answer questions instead of billing having to forward everything.  Most of the issues on this thread seem to be with other email providers (and I've looked for similarities that I can use to diagnosis this issue) but I haven't seen anyone else using Verizon as an email provider talk about this problem. I don't know if the issue has to do with aol took over verizon email or yahoo taking over aol email, but I'm hoping someone can help specifically address why I can't send using the verizon email provider. We use the verizon/aol webpage landing page and not outlook for emails.