Are you planning your BitTitan cutover without accounting for email messages that are in transit when the MX record change fires?

Email messages in transit at the moment of MX record cutover are in one of three states: queued on the sending server waiting to deliver to the source tenant MX, in the source tenant mail flow pipeline being processed by transport rules, or in the source tenant mailbox waiting to be read. BitTitan migration handles content in the source mailbox. It does not handle content still in the transport pipeline when the MX record changes.

Messages queued on sending servers that have already looked up the source MX record will attempt delivery to the source tenant MX for the duration of the sending server retry period, typically 48 to 72 hours. Those messages land in source tenant mailboxes after the BitTitan cutover pass has run. They need to be captured by a subsequent BitTitan pass or forwarded from source to destination mailboxes.

The standard approach: configure SMTP forwarding from all source mailboxes to destination mailboxes for a period of 30 days post-cutover. Inbound messages that arrive at the source tenant after the MX record change automatically forward to the destination. This covers in-transit messages, delayed retries, and any senders who have the old MX record cached.

Have you configured post-cutover SMTP forwarding from source to destination mailboxes to capture email in transit during your BitTitan MX record cutover?

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