Q: Deselect a highlighted message in Mail

We need much more information to give you specific help. Tell us step-by-step, in detail what your actions are.

Tell us a Story

- with a beginning, a middle and end. We need to understand everything that you know and have experienced.

If this issue is new, tell us what immediately preceded its onset - add software, upgrade or update? New equipment?

Quoted from  Apple's "How to write a good question"

   To help other members answer your question, give as many details as you can.

• Include your product (device) name and specs such as processor speed, memory, and storage capacity. Please do not include your Serial Number, IMEI, MEID, or other personal information.
• Provide the version numbers of your operating system and relevant applications, for example "OS X 10.4.11" or "Safari 4.1.3".
• Describe the problem, and include any details about what seems to cause it.
• List any troubleshooting steps you've already tried, or temporary fixes you've discovered.

For a detailed "coaching", please see the User Tips Help us to help you on these forums and Writing an effective Apple Support Communities question