Are you using hotmail / outlook.com?

No, I'm using Mozilla Thuderbird. As far as I know there is only one email address associated with the account.

I have my smart phone synched to my computer email. I'm thinking when I have the email app opened on my phone I get two messages and when I have it closed I only get one. Does that make sense or is it just a coincidence?

And the email address associated with Thunderbird is not Hotmail / Outlook I take it.

What mail provider is it.

Your observation on the timing is intriguing.. Are both using IMAP? What make of phone is it. I have heard of issues with iPhones in the past.

Email address is sbcglobal.net. We use Yahoo as a spam filter then it goes to Mozilla. Phone is an LG Optimus Fuel.

I don't know what IMAP is. How would I check? All I see is a reference to Microsoft Exchange, whatever that is.

OK, says outgoing via ATT is SMTP.

Your phone may well be using Exchange activesync.

In Thunderbird Right click the account, select settings and server settings. The first thing in the dialog is IMAP or POP.

so is is SBCGLobal or Yahoo that you have configured in Thunderbird / Phone?

I am quite concerned about the use of yahoo as a spam filter. Their filtering is poor at best in my experience and telling it something is not spam appears to be about impossible.

Inbound is ATT POP. Outbound is ATT SMTP.

We haven't had any problems with Yahoo.

I use my sbcglobal.net address for both Yahoo and Thunderbird email servers. I don't have any other email addresses.