KoltrixWhat to Do With the Old Mailbox After You Migrate
The MX records have moved and new mail is flowing. Now decide what happens to years of old email: keep it, export it, archive it, or let it go, and when.
On this page(7 sections)
The cut-over went fine. New mail lands in the new provider, the team is replying from it, and nobody's complaining. Then someone asks for the contract thread from two years ago, and you realize the migration isn't really finished. The old mailbox is still sitting there, still billing you, holding years of history nobody has decided what to do with.
This guide is about that decision.
First: don't rush it
The most expensive mistake at this stage is cancelling the old account too early. Once a provider deletes a mailbox, it's usually gone for good. Keep the old account active, at least on its cheapest viable plan, until you've worked through the steps below.
A sensible default is to keep the old mailbox read-only for 30 to 90 days after the cut-over. That window catches stragglers: mail sent to the old servers by senders with stale DNS caches, forgotten forwarding rules, and the "where did that email go?" questions that arrive during the first few weeks.
Your four options
Every old mailbox ends up in one of four states. Most companies use a mix, depending on the mailbox.
| Option | Good for | Cost | Risk |
|---|---|---|---|
| Keep the old account running | Short transition periods, active legal holds | Ongoing subscription | Paying for something you rarely use |
| Import into the new provider | Teams who want one searchable place | Migration effort | Not every provider offers an importer |
| Export to an archive file | Long-term retention at low cost | Storage and some setup | Archives that nobody can search or open |
| Delete | Mailboxes with no business value | None | Losing something you later need |
Keep it running
Simple and safe for a few months. Some providers have a cheaper archive-only or reduced-storage plan; check before you assume you have to keep paying for full seats. Remove the old provider from your MX records, but leave the accounts alive so people can log in and search.
Import it
If your new provider can pull mail in over IMAP or accept an archive upload, importing keeps everything in one place. Be honest with yourself about whether you need it, though. Most teams search their old mail a handful of times a year. Importing ten years of newsletters and notification emails just moves the clutter.
Not every provider offers this. Koltrix, for example, doesn't have a mailbox importer in its first release; an IMAP importer is planned for the following release. If your new provider is in the same position, the export route below is the practical answer for now.
Export to an archive
This is the long-term answer for most companies. The common formats:
- MBOX is a plain, widely supported format. Google Takeout produces one MBOX file per mailbox. Thunderbird and many archiving tools can open it.
- PST is Microsoft's format, produced by Outlook and Microsoft 365 export tools. Outlook opens it natively; other tools can convert it.
- EML files, one per message, are easy to work with in scripts but awkward in bulk.
Whatever you choose, test that you can open and search the export before you cancel anything. An archive you can't read isn't an archive.
Delete
Some mailboxes genuinely aren't worth keeping: a test account, a former employee's mailbox whose contents were all copied into shared threads years ago, a role address that only ever received spam. Deleting them is fine, as long as someone with authority has signed off and you've checked for retention obligations first.
Retention: what you might be required to keep
How long you need to keep business email depends on your country, your industry and your contracts. Accounting and tax records, employment matters and anything under a legal hold may come with specific retention periods. This isn't legal advice, and the rules vary a lot by jurisdiction, so if you're unsure, ask your accountant or lawyer before deleting old business correspondence.
A simple, defensible approach for a small company:
- Identify mailboxes that hold financial, contractual or HR correspondence.
- Export those to archives and keep them for the longest period that applies to you.
- Record what you kept, where, and until when.
- Set a calendar reminder for the deletion date, and actually review it when it comes up.
Where to store archives
Archive files contain years of customer, financial and personal information. Treat them as sensitive:
- Store them in a company-owned storage account, not a personal drive.
- Encrypt them, either through the storage service or by encrypting the files before upload.
- Limit access to the few people who might need to search them.
- Keep two copies in different places if the contents really matter.
- Write down the format and the tool needed to open them, so the next person isn't guessing.
Making archives searchable
The usual complaint about archives is that nobody can find anything in them. A few practical options:
- Open MBOX files in a desktop client like Thunderbird when you need to search. Slow for huge archives, but free and reliable.
- Keep a small "important threads" folder in the new provider. During the transition, forward or re-send the dozen threads people actually reference: key contracts, vendor agreements, the customer escalation everyone remembers.
- Name archives clearly:
2026-09-old-provider-support-at-example.mboxtells the next person what's inside without opening it.
Clean up the loose ends
Before you finally cancel the old provider, run through these:
- Every mailbox has a decision: kept, imported, exported or deleted
- Exports have been opened and spot-checked
- Forwarding rules on the old side are removed or replaced
- No app or device is still sending through the old provider's SMTP
- The old provider is removed from your SPF record
- Old DKIM selectors are removed after a few weeks, once no mail is being signed with them
- Admin accounts on the old provider are documented until closure
- Billing is cancelled, and the final invoice is saved
Removing the old provider from SPF matters. Leaving it in means mail sent from the old system would still pass authentication, which is exactly what you don't want once you've left. If you're not sure what else still sends as your domain, our guide to inventorying every sender walks through finding them.
Key takeaways
- Keep the old account alive and read-only for at least a few weeks after the cut-over.
- Decide per mailbox: keep, import, export or delete. Most companies use a mix.
- MBOX and PST exports are the practical long-term answer when your new provider can't import.
- Check retention requirements with your accountant or lawyer before deleting business mail.
- Store archives securely, test that they open, and clean up SPF, DKIM and forwarding before cancelling.
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