The first sentence in a letter (especially a business letter) should make clear what the letter is about. (See Colloquium's post.) Although with emails the subject line can go some ways toward explaining things it is still a good idea to make sure the reader knows what you are talking about. Perhaps:
This is with regard to last week's email in which you advised the factory of the sequence serial number. Could you please forward that email to me? Please forward to me all emails that have to do with shipping or inspections (i.e. shipping mark, schedule, golden sample, factory audit & cargo status etc). What's a golden sample?
Please note that our customer is required to perform the evaluation of the production of PO xxx. Please kindly advise us of your production start date as per our arrangement. Please follow the sequence serial numbers according to Elsa’s instructions.