* No definitive list: There's no single, universally accepted list of all English words. Dictionaries vary in their comprehensiveness, and new words are constantly being created.
* Word boundaries: What counts as a "word" can be subjective. Do we include proper nouns, technical terms, slang, and obsolete words?
* Frequency: The letter "E" is the most common letter in the English language, so it's likely to appear in a very high percentage of words.
However, you can say with certainty that a vast majority of English words contain the letter "E".