If you are experiencing discrepancies between how your email looks in the Jeto preview (and even possibly the Marketo preview) and the way the final email looks in your inbox, it is most likely due to styling being carried over from the original source where the content was copied from.
Rich text fields allow for styling but can also capture some latent HTML styling from other sources if you copy/paste your text. Different email providers will have different ways of rendering this code and it can cause discrepancies in font style, color, or spacing. To avoid this, simply paste your content without formatting.
If you are using the New Editor (Beta) you will be asked to choose to keep or remove formatting when you paste new content. You will need to choose Remove formatting. This will ensure that no latent HTML is carried over.
Once pasted, any minor formatting such as bold text or bullet points will need to be done in the editor.
If not using the New Editor (Beta) then please follow these instructions.
If you are using a MAC, you can do this by either hitting command + shift + v or by using the paste-and-match style option when right-clicking on your mouse.
If you are using a PC, you can do this by hitting control + shift + paste or by using the paste without formatting option when right clicking on your mouse.