· I appreciate you reaching out to me. · Thank you for getting in touch.
· I'm afraid I would not be able to help you out, even though it sounds like a great opportunity.
· Unfortunately, I'll have to pass even though I've always wanted to attend one of your events.
· As much as I'd love to help, I don't think I'm the best fit due to...
每个人都有自己的优先级，但对方总觉得最重要的依然是他/她的事，这时候你如果说"I'm extremely busy"会让对方觉得你敷衍、爱摆架子。所以，理由这么写，才会让人心服口服：
· Considering my existing workload with the three projects, my plate is a little too full for me to take this on right now.
· Taking into account my extremely packed schedule for the next few weeks, it will be irresponsible of me to say yes to your project that requires at least four hours per day.
· Since my team is currently dedicated to [some existing projects], we simply do not have enough capacity to sufficiently support you.
· I've got three projects on my plate right now. It's unlikely to set aside enough time and resources for...
· I'm more than happy to put you in touch with XYZ, who might be able to help you out.
· My colleague XYZ, quite experienced in this field, may have some insights to share.
· I understand that this is among your top priorities. So if you are able to postpone a few of the deadlines, we could probably add this to our plates.
· If it is possible to deploy extra manpower and resources on this new project, I think it will probably work.