英语商业问候信有一个大客户,之前有联系过,现在很久没联系了,想给他写一封问候信,不知该怎么写?

Dear Sir or Madam
I'm writting this letter to say sorry for I've long time done connect with you.because i've been busy lately.
I'm very glad to made a lot of good deal with your company so long.and we are always kind and honest to each other.so im looking forward to we can talk about commercial and something else next time.
your sincerely
rongylli