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.