I’m not sure if this is what you mean for contact suggestions when you are then creating emails ?
Eg: If there are recipients showing in the To: line you don’t need or no longer want, go to “Menu / Settings / Mail / Compose” and click the box marked “Show Recipients”. You can then delete whatever you want from the To: line history field.
If it’s not what you are referring to, can you do an example screenshot of where you are seeing the suggestions ? Blank out anything private.