Temporary Error 18
Occasionally, issues in Yahoo Mail can cause "Temporary Error 18" to appear.
Don’t worry, this error will usually correct itself within a few minutes to a few hours.
Fix the error on your computer
Sign out of Yahoo Mail on all desktop and mobile devices.
Make sure you’re using a supported Web browser and operating system (OS).
- Learn what's suppported by Yahoo Mail.
Clear your Web browser's cache and cookies.
Restart your Web browser.
Sign back in to Yahoo Mail to see if the error is gone.