Original endings for prepositions in Persian

There is a sentence in Persian:پست‌‌چی برایم نامه آورد. The question is why we use ending م in the preposition برایم , which means "for me". Is it the same as for conjugating the verbs such as:

 من اورم 

تو اوری 

او اورد ?

Or is it merging the two words برای + من ? How can be written the preposition "for him"? Is it براید or برایش ?

Comments:

1.)
برایم = برای + من (for me) برایش = for him/her برایت = for you 

2.)
It is called possessive endings. These are the endings for pronouns used in possessive as well as objective cases.

my=> (am) ــَــ ــم (as in: کتابم)
your(one person)=> (at) ــَــ ــت (as in: کتابت)
his,her=> (aš) ــَــ ــش (as in: کتابش)
our=> (amān) ــَــ ــمان (as in: کتابمان)
your(plural)=> (atān) ــَــ ــتان (as in: کتابتان)
their=> (ašān) ــَــ ــشان (as in: کتابشان)

For example, you can say the phrase "my book" :
کتاب من or کتابم
both of them are correct.

Note that you can use possessive endings with both verbs or nouns.
With verbs, these endings are used in the objective case. For example:
دیدش => او را دید

With nouns, they are used to construct a possessive case, as in:
دفترش=> دفتر او

3.)
پست چی برای من نامه آورد= پست چی برایم نامه آورد 

For me=برایم =برای من برایت= برای تو برایَش= برای او برایمان= برای ما برایشان= برای آنها من آوردَم=I brought تو آوردی= you brough او آورد ما آوردیم آنها آوردند