Way back in Sage CRM 6.2 rich text editing was added to allow for the composition and editing of HTML e-mails and e-mail templates.
The editor that was used for this was a third party component called CKEditor. It still is used in Sage CRM 7.3 but has now been updated to the latest version.
One of the changes that has happened is that spellchecking has been dropped from the rich text editor in favour of just using the browsers native spell check ability.
In Sage CRM 7.2 a user has to select the spell check button.
In Sage CRM 7.3 any text is automatically check by the browser.
This is a very minor change but there may be some implications for systems that are upgraded and that have reused CKEditor behaviour in other screens.
Since Sage CRM 6.2 it has been possible to re-use the CKEditor behaviour in screens other than the e-mail editor screens. Customizations have been added to other multi-line text fields to allow for the rich text editing of notes and detail fields.
See the articles
You will need to check each of the screens and fields that use CKEditor but one very important fact is that Sage CRM 7.3 has added a new User Interface theme. If you have used code to add CKEditor into other fields then you will need to especially check that the code is working correctly under the new theme. One of the likely problem areas is that the paths to images and style sheets maybe missing and that images on the CKEditor buttons do not display.