Invoices email problems

We've been using MYOB Account Right for a long time. I currently do invoices and statements on the desktop version of our AccountRight software even though we have an online account I find it easier to work via the desktop rather than online/web interface. For many months now I am experiencing an intermittent problem but it's quite a serious one for our business and clients. When I finish an invoice and click on Send To Email and send the invoice via email I then go into Sent Emails a little while later to  see if the invoice is on the sent emails list. There are two issues happening at different times.

First issue, sometimes invoices sent by email never actually appear on the Sent Emails list. Even up to hours later. Sometimes I check back the next day and still not there. Now I am ok to send it again and again when it never appears on the Sent Emails list, but should I really have to double-check if it comes up as Sent and then go through the process to resend those that don't? It is very time-consuming to do this because I can't trust MYOB email functionality anymore.

Second issue, sometimes invoices sent by email all appear on the Sent Emails list. However, when I reconcile payments and send statements I get a call from the clients to say they never actually received the invoice in the first place. I have had some very concerned accounts folk tell me that they do not like to have invoices listed as outstanding when they have never actually received it. I ask them to check their spam/junk. Nothing. So MYOB says email sent but client says nothing received. Not good.

I have similar issues with payslip emails but I will post that in the appropriate section.

Help please.