How to resolve iCloud storage issue preventing email sending on iPhone?

If you received an email, it was your iCloud storage that was full, not your iPhone Storage.

What's the difference between device storage and iCloud storage? - Apple Support

To help free up space on your iCloud, review the information provided here:

Manage your iCloud storage - Apple Support

"How to resolve iCloud storage issue preventing email sending on iPhone?: I dont seem to be able to send email messages as apparently my iPhone storage is full and an email said it was. I have plenty of storage available but emails are not sending. Please help"

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Clear Space Using my User Tips:

See if you need to clear lots of space. System resources may be using up too much services, making it overheat. Internal storage cannot be upgraded. It is what it is. So, the maximum internal storage capacity never increases, even if you upgraded your iCloud plan.

So, what to do...

Clear Space, Using my User Tips:

• How to Clear Space from your Mobile Device, and What to Clear: - User Tip
• How to Clear "Other" in your iPhone's Storage - Use Backup - User Tip