我万分没有想到您能在百忙之中回复我的信件.英文翻译

I didn't think you are very busy in replying my letter .

I was not think I can you in spite of being very busy toglance reply to my mail

I am not think you can reply my letter in your busy schedule望采纳

I am surprised that you replied my email in your busy schedule.
感觉这么说会合适一些，仅供参考。