Consider an organization which as a high number of users. In this organization, a small minority (usually the top management) need all the collaboration features offered by O365 whereas the rest of the users mainly use only email. In such an organization, there is a requirement to host the email infrastructure of a company across 2 different solutions, such that both the solutions share the same SMTP address space and the company can divide their mailboxes across the two solutions.

For example, in an organization with 1000 users, a typical co-existence between Mithi SkyConnect and Microsoft Office 365 will allow the organization to host 100 users on O365 and 900 on Mithi SkyConnect, sharing a common domain name in their email ids, and with seamless mail flow between the users of both systems.

Mail flow and the checks at different points of contacts

The diagram below shows the mail flow and the point of contacts for a co-existence setup between SkyConnect and O365.

mail flow and the point of contacts for a co-existence setup between SkyConnect and O365.
Note: Though the diagram shows MX records pointing to the SkyConnect server on connection point S0, the co-existance can be configured where the MX will point to the O365 setup as well.

Checks to be done at the different points of contact

Refer to the table below for the recommended checks to be done at the different points of contact depicted in the image above.

Point Of ContactScopeQuarantine Report
O365O1As per O365 policies. Incoming Mail is assumed cleanNA

O2As per O365 policies. Scan for Virus at the minimumNA

O3No checks done. Clean mail expectedNA

O4No checks done. Clean mail expectedNA

Spam, Virus, Malware for all users

Note: The MX can point to O365, in which case the spam, virus, malware protection for all users is provided the O365 system.
Yes (if MX points to SkyConnect. If MX points to O365, refer to the O365 documentation)

S1Virus check (optional)NA

S2DDOS, Rate control, Auth, Spoof, VirusNA

S3No checks done. Clean mail expectedNA

S4No checks done. Clean mail expectedNA

Mail flow

The table below explains the mail flow between SkyConnect and O365 through the point of contacts shown in the image above.

External email idSkyConnect userS0=>LD (Local Delivery)
External email idO365 userS0=>S4=>O1=>LD
SkyConnect userSkyConnect userS2=>LD
SkyConnect userO365 userS2=>S4=>O1=>LD
SkyConnect userExternal email idS2=>S3=>ED (External delivery)
O365SkyConnect userO2=>O3=>S1=>LD
O365O365 userO2=>LD
O365External email idO2=>O4=>ED