I think it's good to do things in tandem. As soon as you've sent your first email to another company discussing potential partnership options, I would recommen

I think it's good to do things in tandem. As soon as you've sent your first email to another company discussing potential partnership options, I would recommend sending an email along the lines of: "Thanks very much for your interest in doing a deal with us. I've looked into your companies background, and I'm really impressed with what you've managed to build. We're definitely looking for opportunities to partner with companies like yourself to expand our potential userbase, since we've had demonstrated success with this particular app we're keen to continue to build on this success and growth. In the interests of being open and upfront, I should let you know that we're in discussions with other companies about potential partnership options. We'll be in touch soon with some more information or questions on how we might be able to move forward." I would recommend sending a message like that. It does a number of good things. 1. Reinforces your interest to work with that particular company 2. Reinforces your app and the success and growth it's having 3. Shows that you're an experienced operator since you're fielding other quotes, and you're a good operator, because you're being up front and honest about it. 4. Shows that you're in no rush to make a deal, and you'll deal with things in your own time. All together that sends quite a powerful message, and lets you start negotiating from a position of strength. Which, really, you're in. You just need to realise it, and communicate it.