If I e-filed, however, I have to mail in form 8283. What does this mean?

[AnthonyJ]

Typically Form 8283 is auto-populated and attached to your federal return.  However, Form 8283 is required to be mailed in IF you have donations over $5000 where a signature of an appraiser and/or a signature of an official of the charity is required.

See the answer posted by Opus 17 (SuperUser):

https://ttlc.intuit.com/replies/5447921