A computer implemented method comprising: receiving , by a processor from a sender electronically coupled therewith, an electronic message comprising data indicative of a queue data structure of a plurality of queue data structures , stored in a memory coupled with the processor , in which the electronic message should be stored to await transmission to a requestor and whether the electronic message is related to another previously received electronic message; storing , by the processor , the received electronic message in the queue data structure grouped together with any related previously received electronic messages which have not yet been transmitted to a requestor ; receiving , by the processor , a request from a the first requestor for transmission thereto of an electronic message from the queue data structure , the request being related to a read transaction by the first requestor of one or more electronic messages from the queue data structure ; identifying , by the processor responsive to the request, an electronic message stored in the queue data structure for which a second requestor has not previously received another electronic message related thereto responsive to a second request received from the second requestor which is related to another read transaction from the queue data structure that has not yet been completed by the second requestor ; transmitting , by the processor , the identified electronic message to the first requestor ; and preventing , by the processor , transmission of an electronic message, related to the identified electronic message, to the second requestor , until the first requestor indicates that its read transaction has been completed. receiving , by a processor from a sender electronically coupled therewith, an electronic message comprising data indicative of a queue data structure of a plurality of queue data structures , stored in a memory coupled with the processor , in which the electronic message should be stored to await transmission to a requestor and whether the electronic message is related to another previously received electronic message; storing , by the processor , the received electronic message in the queue data structure grouped together with any related previously received electronic messages which have not yet been transmitted to a requestor ; receiving , by the processor , a request from a the first requestor for transmission thereto of an electronic message from the queue data structure , the request being related to a read transaction by the first requestor of one or more electronic messages from the queue data structure ; identifying , by the processor responsive to the request, an electronic message stored in the queue data structure for which a second requestor has not previously received another electronic message related thereto responsive to a second request received from the second requestor which is related to another read transaction from the queue data structure that has not yet been completed by the second requestor ; transmitting , by the processor , the identified electronic message to the first requestor ; and preventing , by the processor , transmission of an electronic message, related to the identified electronic message, to the second requestor , until the first requestor indicates that its read transaction has been completed. <EOS>