create submission comment mail replies on correct shard
create submission comment mail replies on correct shard

closes #CNVS-38755

Change-Id: I4c2f12d247f9b569368f4fad21581080a1025f5b
Reviewed-on: https://gerrit.instructure.com/123970
Tested-by: Jenkins
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
Product-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
QA-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

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