Hi paulsger55-gmail Thank for reaching out to us here on the Community. Do you know if customers that you're sending the emails to are actually receiving the emails however you're receiving a not sent error?
There is a thread about ongoing issues with emails being sent from Quickbooks.
Quickbooks should really be making a statement about this as the delivery of invoices to customers is a fundamental part of the process and the suggested work around of manually sending invoices will be far too consuming for many.
Hello SEdmunds, thanks for posting on this thread do you know if customers that you are sending the emails to are actually receiving them but it just shows in your QuickBooks account that they are not sent error?
In my case they haven't been receiving them. Yesterday I found that 8 invoices hadn't been delivered over the last week and found that thread I posted when I began investigating.
The error on mine were Bounced Email.
Manually emailing 7 of the recipients directly I've had replies from them showing there is no problem at the customers end.