E-mailed invoices not being received

I am using Timeslips 2014. 

Under Client Information, Arrangement 2, the boxes to send bills and statements via e-mail are checked.

Under Generate Bills, Options, send bills via e-mail is checked.

When I approve the bills, the box to send via e-mail comes up and the proper e-mail is chosen. 

When I click "OK" and the pop up indicates that the invoice is being sent.  However, the e-mail is never received.

Any suggestions?