To as, doesn't seem ok
in formal letters they use i am writing you to as, ................
but i guess it should be i am writing to you regarding .............

the first sentence doesn't make sence to me

Question

To as, doesn't seem ok
in formal letters they use i am writing you to as, ................
but i guess it should be i am writing to you regarding .............

the first sentence doesn't make sence to me

Answer

I think the words are jumbled and it should be 'I'm writing to you as'. In this case 'as' means 'because', for example 'I'm writing to you as I read your question on italki'. 
If the words really are in that order, then you're right, it doesn't seem to make sense.