Email Flashing

Hello,

I am having a problem with the native Apple Mail app on my MacBook Air. I will be surfing the internet in Safari and want to send a link to someone. I will use the "Share" button in the upper right on Safari and choose to send it as an email. This will open up the native Apple Mail app and past it in as a link. Almost immediately it starts to flash between that email and another random email. I cannot get it to stop and have to force quit the Mail application. Does anyone have this problem and how can I fix the problem. I've looked at the online community, but cannot find anything that matches my specific problem. I currently am running a MacBook Air with macOS High Sierra.

Thanks for your help.