Hi there coleen71,
To confirm, you'll be replying to an email and see "null" somewhere on your iPad, but changing your email address to the one email address you used to use with iCloud helps. Does that sound correct? Also, where are you seeing "null"? Are you seeing that in the reply or the thread? Your answers can help us make sure we fully understand what's going on, which can help us determine possible next steps.
Also, if you haven't already, you can see if restarting your iPad may help, which may seem like a simple step but it can sometimes help resolve unexpected issues:
"How to restart an iPad with a Home button
- Press and hold the top button until the power off slider appears.
- Drag the slider, then wait for 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
- To turn your device back on, press and hold the top button until you see the Apple logo."
Those steps are from this article: Restart your iPad - Apple Support If your iPad doesn't have a Home button, that article has steps for those types of iPad devices as well. Let us know if that helps or if you've already tried that step.
Take care!