US Patent 11025572 Electronic mail delivery system having a spool function

A computer-implemented method includes receiving, by a first mail transfer agent having a first spool, an electronic mail. The computer-implemented method further includes issuing, by the first mail transfer agent, a first unique identifier to be associated with the electronic mail. The computer-implemented method further includes holding the electronic mail in the first spool for a first predetermined period of time. The computer-implemented method further includes transferring the electronic mail from the first spool to a second mail transfer agent having a second spool. The computer-implemented method further includes issuing, by the second mail transfer agent, a second unique identifier to be associated with the electronic mail. The computer-implemented method further includes holding the electronic mail in the second spool for a second predetermined period of time. The computer-implemented method further includes prohibiting a transfer of the electronic mail from the second mail transfer agent to a mail recipient agent.