two copies of sent emails

I’m not sure what’s causing this but it appears that there are two copies of sent emails whenever I send something. I don’t know what I’m doing (if anything) to trigger this, but it seems to be happening when I’m sending emails with attachments. 

With that said, I’ve been getting reports that some of my emails are not getting received. And so I’m wondering if this would have anything to do with my client making it seem as though I’m spamming mail servers by sending multiple emails to clients. 

Any ideas what would cause this and how I can fix it? 
This only seems to have started with my newer email client.