breaking down this compound+complex sentence

[lingga]

Would you help me with this sentence I found in one of the IELTS practices reading article?

'Addressing your letters properly and using the postcode is important, and will ensure your letters are delivered quickly and accurately.'

in my understanding:
', and will ensure your letters are delivered quickly and accurately' is the second independent clause.
what I'm not sure:

• why there is no subject or at least a pronoun (it) between the coordinate conjunction (, and) and the auxiliary verb (will)
  why to be (are) which is in the present condition is used, even though there is to be (will) which is referring future condition already used in the first place
  Does this one (, and it will ensure your letters be delivered quickly and accurately.) make more sense?

I'm not a native speaker, and I'm preparing myself for an IELTS test at this moment. Perhaps I can improve my writing skill with this forum. Thank you

[Josef Essberger]

why there is no subject or at least a pronoun (it) between the coordinate conjunction (, and) and the auxiliary verb (will)

But there IS a subject:

Addressing your letters properly and using the postcode is important, and [addressing your letters properly and using the postcode] will ensure your letters are delivered quickly and accurately.

The subject [in square brackets] is "understood".