Abstract: The disclosure describes a system that assigns an internet protocol (IP) address to each of one or more tenants, establishes an inbound connection with each of one or more tenants, and identifies each of one or more tenants based on the IP address and a destination address associated with the each of one or more tenants. The system further establishes an outbound connection with the each of one or more tenants, receives one or more commands and a message from each of one or more tenants, and determines an email address of at least one first tenant, of the one or more tenants, based at least in part on the one or more commands and the message. The system further updates one or more email addresses in one or more message headers with the domain of the at least one first tenant, and transmits the message to the at least one first tenant during an overlapping simple mail transport protocol (SMTP) session.