Most of my received emails are stating storage is full but I am only using 70 of 256 that I am paying extra for

See the section If you can't send mail from the Mail app on your Mac

in the article If iCloud Mail isn't working - Apple Support

What is the exact error message your correspondents are seeing?

The error message may be referring to the local storage on your device and not to the iCloud storage at all.

Even with plenty of free iCloud Storage you may be filling the local storage on your device with documents and data that are stored locally on the device. Try to delete old mails with large attachments, or check, if your Photos Library is using large amounts of local storage. This can happen, if not yet all photos have become optimised and replaced locally by smaller, light-weight versions. How much free storage do you have locally on the device?

Can you post a screen shot from mail application , take cursor on window > click on connection doctor ( hide your mail address before posting ) .