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Email Migration Readiness Check

Email migrations rarely fail on the copy itself. They fail on the things around it: a forgotten shared mailbox, a DNS record with a long TTL, mail that lands in spam because of a missing PTR record, a backup nobody has restored. Answer for the migration you are planning, whether to a self-hosted server or to a new provider; the gap list shows what to fix before cutover.

1. Have you listed every mailbox, alias, shared mailbox and distribution list, with each one's size?
2. Do you know the total data size and have you timed a real copy of a sample mailbox at your actual bandwidth?
3. Will the MX record's TTL be lowered, to something like 300 seconds, at least 48 hours before cutover?
4. Are SPF, DKIM and DMARC prepared and tested for the new server before the first real message goes out?
5. Is outbound port 25 open from the new server, and has the IP address been checked against blocklists?
6. Do the mail hostnames have TLS certificates with automatic renewal, and do clients find the server through autodiscover or autoconfig?
7. Have you migrated a pilot group, including folders, flags, calendars and contacts, and compared the result with the source?
8. Have you restored a single mailbox from backup on the new server at least once?
9. Are spam and virus filtering, rate limits and monitoring for queue length and disk space switched on?
10. Is there a rollback plan, with the old system kept available read-only for a defined period and users told the date and what to do on their devices?
Readiness score

Gaps, with what ready looks like

    Where these questions come from

    They are the steps that decide whether a mail cutover is uneventful: inventory, measured copy time, a short DNS TTL, authentication records, deliverability basics, certificates, a pilot, a tested restore, monitoring and a rollback path. They come from the migrations we have run and written about, and they apply to any destination, not only ours.

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