A method of processing a message for a subscriber session, wherein the message comprises a Fully Qualified Domain Name, FQDN, of an originator of the message, wherein the originator is located in a first network domain and wherein the message is directed towards a destination in a second network domain, the method comprising: receiving the message; determining the FQDN comprised in the message; determining an identifier associated with the message, wherein the identifier comprises at least one of a subscriber identifier, a session identifier and a destination identifier; applying a cryptographic operation on the FQDN and the identifier, or on information derived therefrom, to generate a cryptographic value; processing the message by substituting at least a portion of the FQDN with the cryptographic value; and forwarding the processed message towards the second network domain, wherein the cryptographic operation is configured so that the number of different cryptographic values that can be generated is limited to a maximum number by: applying a first hash function to hash the FQDN of the originator, or a portion thereof, to obtain a first hash value; mapping the first hash value on a predefined range defining the maximum number of exposed addresses for a given originator to obtain a spread value; applying a second hash function to the spread value and the identifier associated with the message to obtain a second hash value; and encrypting the second hash value with a cryptographic key to obtain the cryptographic value. receiving the message; determining the FQDN comprised in the message; determining an identifier associated with the message, wherein the identifier comprises at least one of a subscriber identifier, a session identifier and a destination identifier; applying a cryptographic operation on the FQDN and the identifier, or on information derived therefrom, to generate a cryptographic value; processing the message by substituting at least a portion of the FQDN with the cryptographic value; and forwarding the processed message towards the second network domain, wherein the cryptographic operation is configured so that the number of different cryptographic values that can be generated is limited to a maximum number by: applying a first hash function to hash the FQDN of the originator, or a portion thereof, to obtain a first hash value; mapping the first hash value on a predefined range defining the maximum number of exposed addresses for a given originator to obtain a spread value; applying a second hash function to the spread value and the identifier associated with the message to obtain a second hash value; and encrypting the second hash value with a cryptographic key to obtain the cryptographic value. applying a first hash function to hash the FQDN of the originator, or a portion thereof, to obtain a first hash value; mapping the first hash value on a predefined range defining the maximum number of exposed addresses for a given originator to obtain a spread value; applying a second hash function to the spread value and the identifier associated with the message to obtain a second hash value; and encrypting the second hash value with a cryptographic key to obtain the cryptographic value.