It depends on what office you are going through. For example, Accra has a 40% refusal rate, so I sent in 400 pages of communication evidence (emails, texts, phone bills, chat logs and copies of postcards/letters)
You also have to think about how long your relationship has been going on. If it's a short time, you send more evidence. If you've only met your spouse one or two times in person, obviously you will need more evidence.
Generally though, I think one or two emails per week of your relationship would be sufficient. Try to find ones that show you were communicating about your relationship, your future plans, about friends/family members, and of course some 'love letters' if you have them.
Each case is individual, so do what you think is best to clearly communicate to the IO that yours is a loving and genuine relationship.