Question: I wonder if there are any good websites or apps which provide expressions for use in emails. Answer: There are useful websites like Grammarly which help people to correct their writing as they write. Some of my students use these are find them very useful. But if you want to improve your written English, the best thing to do is to focus on ‘functional chunks’ which can be used in practical contexts such as email writing. I recommend taking a Business English course with a tutor (hello!). You could perhaps using a textbook such as Market Leader or Business Result (I prefer the latter).