What Is the Yellow Triangle Warning in Outlook Express When Sending?by ErinB ; Updated February 10, 2017
Windows software uses a yellow triangle icon with an exclamation point to represent that an error has occurred. To ensure an email is properly sent, troubleshoot the issue immediately. The error may have something to do with HTML coding, a wrong email address or antivirus software.
HTML Coding Error
Common HTML coding errors include Server Errors, which are represented by the number "500" along with the error icon. Another common HTML error is the Out of Resources error represented by the number "503." This error may be caused by a system overload and is most likely not a permanent issue.
Incorrect Email Address
The forwarding address to which an email is sent may be incorrect. If so, Outlook Express will detect this by using the error symbol. Be sure to verify the email address to which you are sending the email.
Your antivirus program may be scanning emails, causing the message to timeout. Delete unknown or suspicious emails. According to Outlook Express Help, "Antivirus software can trigger the destruction of an entire message folder or the entire message store, when it attempts to remove a message containing a potential virus." Your antivirus program may be working too hard to ensure infected messages are not being sent or received by your inbox.
Verify the Internet connection and the account settings. If the issue it not resolved, contact the Microsoft website at the Product Solution Center.