Reading others letters..

In the name of Allah, We praise Him, seek His help and ask for His forgiveness. Whoever Allah guides none can misguide, and whoever He allows to fall astray, none can guide them aright. We bear witness that there is no one (no idol, no person, no grave, no prophet, no imam, no dai, nobody!) worthy of worship but Allah Alone, and we bear witness that Muhammad (saws) is His slave-servant and the seal of His Messengers.

Allah Says in the Holy Quran Chapter 49 Surah Hujuraat verses 12-13:
12 O ye who believe! Avoid suspicion as much (as possible): for suspicion in some cases is a sin: and spy not on each other nor speak ill of each other behind their backs. Would any of you like to eat the flesh of his dead brother? Nay ye would abhor it...but fear Allah: for Allah is Oft-Returning Most Merciful.
13 O mankind! We created you from a single (pair) of a male and a female and made you into nations and tribes that ye may know each other (not that ye may despise each other). Verily the most honored of you in the sight of Allah is (he who is) the most righteous of you. And Allah has full knowledge and is well acquainted (with all things).

Sunan of Abu-Dawood Hadith 1480 Narrated by Abdullah ibn Abbas
The Prophet (saws) said: 'He who sees the letter of his brother without his permission, sees Hell-fire!'

In light of the above absolutely clear guidance of Allah and His Messenger (saws), it is not permissible and an abhorred and detestable act in the Sight of Allah for one to read the private letters of another without their precise permission and will.

If one trusts, obeys, and follows the guidance and commands of Allah and His Messenger (peace be upon him), one can be assured of never ever being misled; but if one believes, obeys and follows any other guidance, other than that of Allah and His Messenger (peace be upon him), one can be assured of being led astray

Whatever written of Truth and benefit is only due to Allah's Assistance and Guidance, and whatever of error is of me alone. Allah Alone Knows Best and He is the Only Source of Strength.