Do emails take up iCloud storage?

Hi, my problem is a bit more complex then it seems at first

I have a gmail account and an icloud-mail side-account.

All my gmail mail is forwarded to my iCloud. I also configured my SMTP server setting so messages sent out from iCloud are sent from the gmail adress.

This mail account isn’t tied to my normal Apple ID - in settings > accounts I added a new iCloud account, selected „create a new Apple ID” and then „I don’t have an email adress” in order to get one.

Now, the additional Apple ID is in my settings, looking like an ordinary email account.

I can’t see any iCloud-storage-related settings page. Does this mean Apple’s generous and it’s unlimited if you only use mail? Or does it mean one day I’ll just stop getting emails? If the storage is limited, is there any way to expand it?

On my main account I have a 50GB plan. I can change it to 200, and then add my other Apple IDs as family members so they can share my storage.

I’d rather not do that, since 200GB is way more then I need and it’s 3 times more expensive then my current plan...

...so, yeah. That’s the question.