Can IMSS 7.1 SP1 configure its own relay restrictions if a third-party upstream server is not installed?

No. IMSS 7.1 cannot configure its own relay restrictions as it does not have its own MTA on the Linux platform. You can only configure relay restrictions using a third-party MTA.

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Can IMSS 7.1 SP1 configure its own relay restrictions if a third-party upstream server is not installed?