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Hello cndavis.

Let's do some testing to narrow down the issue.

Safe mode will tell us if the issue is related to a startup item or plugins, and sometimes corrects the issue. This article will tell you how: Use safe mode to isolate issues with your Mac

If everything is working correctly in safe mode, but is not working when you get back to your user account, please check the section titled "If an issue doesn't happen in safe mode" for the next troubleshooting steps.

If the issue continues while in safe mode, a test user will let us know if the issue is isolated to your account, or system wide: How to test an issue in another user account on your Mac. If the issue happens in the test user also, then please check the section titled "If an issue happens in more than one user account."

If the issue continues, let us know the results of each of these tests. 

Cheers.

Hello and welcome to Apple Support Communities, cndavis.

If I understand your post correctly, you are trying to update your signatures in Mail on your MacBook Air. I’d like to help.

To create a new signature, follow the steps in this article:

Create and use email signatures in Mail on Mac

If you are trying to change signatures currently being used, follow these steps:

Change Signatures preferences in Mail on Mac

Let us know if that resolves this issue for you. 

Thanks for using the Apple Support Communities. Take care.