CiviMail error: "Sorry an error occurred and your information was not saved"
I've run into this error for three reasons:

1: I copied and pasted in text and there was a special character in there that CiviCRM did not like. I figured out which one it was by pasting in only pieces of the text and watching to see when it quit saving and instead gave me the error.

2: I'd upgraded CiviCRM and the permissions weren't correct on some files (I'm logged in as root and therefore have to change owner/group when I upload).

3: A modsecurity issue. My host was able to look at the logs and whitelist the URI that was causing the issue. Last time it was: /civicrm/ajax/rest