A method performed by a receiving Public Land Mobile Network (PLMN) (MNO 2) including at least a receiving node, the method comprising steps of: said receiving node: receiving from a foreign delivery entity source node in a foreign PLMN (MNO 1) a MT message having an originator and having a recipient, extracting from said message an MSISDN of said originator and an address of said foreign delivery entity source node and performing validation steps of: (a) performing an SRI-for-SM operation for the extracted originator MSISDN on a foreign location register having a foreign location register address, and in case of a negative response with an error code indicating an unavailable number, determining a potentially forged originator MSISDN, in case of a positive response, receiving the location and the IMSI of the originator MSISDN and using the received IMSI to verify association of the originator with the foreign network, (b) verifying association of said foreign source node with said foreign location register by comparing said foreign location register address with said foreign delivery entity source node address, including identifying said foreign location register address according to SCCP CgPa GT address digits of said foreign location register, and using said digits to compare said addresses of said foreign location register and said foreign delivery entity source node, wherein said validation steps (a) and (b) are performed before attempting to perform tasks for delivery of the message. receiving from a foreign delivery entity source node in a foreign PLMN (MNO 1) a MT message having an originator and having a recipient, extracting from said message an MSISDN of said originator and an address of said foreign delivery entity source node and performing validation steps of: (a) performing an SRI-for-SM operation for the extracted originator MSISDN on a foreign location register having a foreign location register address, and in case of a negative response with an error code indicating an unavailable number, determining a potentially forged originator MSISDN, in case of a positive response, receiving the location and the IMSI of the originator MSISDN and using the received IMSI to verify association of the originator with the foreign network, (b) verifying association of said foreign source node with said foreign location register by comparing said foreign location register address with said foreign delivery entity source node address, including identifying said foreign location register address according to SCCP CgPa GT address digits of said foreign location register, and using said digits to compare said addresses of said foreign location register and said foreign delivery entity source node, (a) performing an SRI-for-SM operation for the extracted originator MSISDN on a foreign location register having a foreign location register address, and in case of a negative response with an error code indicating an unavailable number, determining a potentially forged originator MSISDN, in case of a positive response, receiving the location and the IMSI of the originator MSISDN and using the received IMSI to verify association of the originator with the foreign network, (b) verifying association of said foreign source node with said foreign location register by comparing said foreign location register address with said foreign delivery entity source node address, including identifying said foreign location register address according to SCCP CgPa GT address digits of said foreign location register, and using said digits to compare said addresses of said foreign location register and said foreign delivery entity source node,