Business Email on Exchange Online
Migration goes wrong in a small number of predictable ways. All of them are avoidable.
Email migration has a reputation it no longer deserves. The failures follow a short list of patterns — an overlooked SPF record, a website form still sending through the old server, forwarding rules nobody documented — and every one is avoidable with preparation.
The records that decide whether mail arrives
Four DNS records govern delivery and trust: MX for where mail is delivered, SPF for which servers may send on your behalf, DKIM for signing, and DMARC for what receivers should do when the checks fail.
SPF is where migrations most often go wrong. There must be exactly one record listing everything that legitimately sends for your domain, including website forms and marketing tools. Two records produce failures that are awkward to diagnose.
Pre-migration audit
Mailbox sizes, shared and distribution addresses, forwarding rules, and who actually controls the domain registration.
Cutover planning
TTL lowered ahead of the change so it propagates in minutes rather than trickling over a day.
Authentication
SPF, DKIM and DMARC configured together, since each without the others leaves a gap.
Post-migration checks
Mail arriving, the website form still working, and shared addresses reaching the right people — verified before anyone else notices.
The parts people forget
Shared addresses — info, sales, accounts — are frequently overlooked and are often the ones customers actually use. So are forwarding rules set up years ago, which do not migrate and whose disappearance is discovered by whoever relied on them.
Keep the old mailboxes intact for a few weeks afterwards. They cost little and they are the answer to 'I cannot find an email from March'.
Exchange Online Email — Frequently Asked Questions
Will we lose emails during migration?+
Properly run, no. Mailbox data is copied before the switch, and mail arriving during the changeover queues at the sending server and is delivered once DNS settles. Delays of minutes are normal; loss is not.
How long does it take?+
Preparation is usually a few days and the changeover a single evening. The variable is mailbox size and connection speed, since data has to transfer before the switch.
What is the most common problem?+
An existing SPF record that is overlooked. There must be exactly one, listing everything that legitimately sends for your domain including website forms and marketing tools. A second record causes delivery problems that are hard to diagnose.
Will our website contact form still work?+
Only if it is reconfigured. Forms sending through the old mail server stop silently after migration, and it is usually noticed when enquiries stop arriving. Test it the same day.
What about shared mailboxes like info@ or sales@?+
They migrate, but they are the ones most often forgotten in planning — and frequently the addresses customers use most. They belong in the pre-migration audit.
Should we keep the old hosting?+
For a few weeks, yes. It costs little and answers questions about older messages while people settle in. It does not need to stay in daily use.
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