Decrypt a message

Probably PGP, although could you ask the sender to tell you how it's encrypted, and to send you his/her public key?  You can import this into Outlook and have it automatically decrypted.

Are you sure it's encrypted and not just MIME encoded?

You should take public key officially. Otherwise it will illegal.

BR Dushan

And Private key.

Thanks for all help.
What a pity! I know little information: encrypted message, plaintext's characters are numbers

Dushan911 - What do you mean private key?

A private key should not be shared......

Questoiner want to decrypt.

Dushan -

with public key encryption systems the send can encrypt with her private key and then anyone can un-encrypt with her public key - this proves the message came from her - signing.

to ensure only you can read it she can encrypt it with your public key then only you can un-encrypt it with your private key - this provides the secrecy part.

hence public key encryption services can provide signing, confidentiality or both.

never reveal your private key.

this is an incredibly simplified explanation as it is a bit of an aside from the original question.

Searching the internet, I found some discussion 'bout similar this. Encrypted message are all hexa character, and it 's used RSA Crypto system. Does it true in this problem?

Technically, it's possible to deccrypt more or less anything, but bear in mind this is illegal in most countries unless you have the sender's permission.  This is why you need the sender's public key.  If you have this, then you have permission to decrypt the email (as long as it was sent to you).
Are you intents benign, or are you trying to decrypt something you've not been given permission to read?
Otherwise, I don't see what the problem is with getting the sender's public key?