Ouch! To quote another member, "That is a sticky widget."
Seriously, do you remember composing the messages, or letters? If so, then own up to it, and your mate either believes you or not. If you got caught doing something, own up to it. This is a perfect example of not knowing what products you use, and the dangers of the uses of such products. I can tell you stories of customers asking me why their IPHONE pictures are showing up on their TV'S. Wow, maybe you shouldn't have bought that APPLE TV!
OK, so if you are the only one that has access to the account......then explain the mail, and explain that you cannot explain the dates! If your "partner" is truly your partner, then they should realize that you trust them to listen and trust you. Or what is the point.
Go and get her a dozen Roses, and explain that you cannot explain the dates, but you can explain the drafts. Once again, you do trust that you two are partners, don't you?
I have been in the game for longer than a bank robbery sentence (never say that with your wife present), and I have learned that you have to talk, and listen, and trust. You may not like what you hear, and they may not like what they hear, but the point is the communication is there and you are part of it!
To quote another member, "What was the question?"