New | Email to Case Premium
Attempting to send a new comment over 32,000 characters will currently result in an error message on the New Comment page, preventing the user from successfully sending. I suspect this is in line with current character limit of the Most Recent Public/Private Comment HTML fields in Email to Case Premium, which stores just over 32,000 characters.
Although these are managed fields, Salesforce allows the administrator (of the Org which the app is installed into) to adjust the length of these fields, up to 1,638,400 characters for the Case object. (The amount of character length left will depend on other custom rich text/long text area fields already on the object.)
For organizations that require the need to send larger comments, we should encourage those clients to adjust the field length on those respective fields, and only enforce a limit on the New Comment page only if it exceeds that updated limit.