If you want to resolve your sending issue in At&t then quickly follow this post to troubleshoot you’re all problems regarding At&t.
1) First go to your At&t email account through your email address and password. Make sure an expected email didn’t stay in your spam folder. After that go to your setting which is located top right side of the page. Now search for “blocked address” section and ensure that there is no address from which you would expect email. After that you have to review the filter to confirms that the mail is arrives in correct folder. Now log you immediately from your account and log in again.
2) Always prefer supported browser for your At&t email account such as: internet explorer, Google chrome, safari etc.
3) If problem is again encountered than, clear your cookies and cache. For this:
• First you have to launch your browser
• Then press CTRL+SHIFT+DELETE & choose the item which you want to clear from the history
• You can choose clear or delete button depending on your browser type
• Then just close your browser for some time and re-start your web browser.
4) Your java script or adobe flash player is enabled or up to dated.