How to Move Outlook Email to Thundermail (2026)

To move Outlook email to Thundermail, export your Outlook mail to a PST, create a Thundermail app password, then upload the PST to Thundermail over IMAP with a converter. Use the Thundermail server on port 993 with SSL/TLS, your address and the app password. The Outlook folders, dates and attachments arrive in Thundermail. Outlook does not need to stay open during the move.

Moving email services is where people lose years of mail, because most web interfaces import little and the rest gets left behind. Outlook to Thundermail does not have to go that way. Outlook can hand its mail to a PST, and Thundermail can take mail in over IMAP, so a converter bridges the two.

The move runs in one direction: read the Outlook PST, write to the Thundermail account. The steps below cover the PST export, the app password and the upload, then the questions people raise before switching services.

📋 On This Page

Why Route Outlook to Thundermail Through a PST?
How Do I Move Outlook Mail to Thundermail?
Do My Outlook Folders Come Across?
What About Outlook Rules and Settings?
Which Outlook to Thundermail Route?
Outlook to Thundermail Questions

Why Route Outlook to Thundermail Through a PST?

Thundermail has no button that reads an Outlook profile, so the mail needs a form both sides understand. A PST is that form. It is Outlook's own mailbox file. It holds every folder and message, and a converter can read it without Outlook in the way. From the PST, the same converter writes the mail into Thundermail over IMAP.

The alternative is dragging messages between two open accounts, which is slow and tends to lose the folder tree. Going through a PST keeps the structure and lets one pass carry the whole mailbox. It also keeps the mail on your machine right up to the moment it lands in your Thundermail account.

How Do I Move Outlook Mail to Thundermail?

Four steps, about twenty-five minutes plus the upload. The PST export is first, then the app password, then the transfer.

Classic Outlook Export Outlook Data File wizard with Include subfolders checked beside a Thundermail IMAP card. — In classic Outlook, select the mailbox or folder to export and keep Include subfolders checked when you need the full tree. Uploading the exported mail to Thundermail is a separate step.

Get your Outlook mail into a PST

Export from Outlook, or use an existing PST

Thundermail reads a mailbox file, so start with a PST. If your mail is in Outlook now, export it with File, Open & Export, Import/Export, then Export to a file and Outlook Data File. If you already hold a PST, an OST or an archive, you can use that instead and skip the export.

Set up a Thundermail app password

Needed for any tool to sign in

Sign in to the Thundermail dashboard and open the Email Settings area. Use the app password control to create one, then save it in a safe place, because Thundermail reveals it a single time. Your normal login password will not work for a migration tool, so this app password is what the transfer uses.

Load the PST and point it at Thundermail

IMAP destination with the Thundermail server

Open Univik Email Converter, add the PST and choose the IMAP destination. Enter the Thundermail server on port 993 with SSL/TLS, your full address for sign-in and the app password. The converter reads the PST with no need for Outlook running and prepares to upload it to your Thundermail account.

Run the migration and open Thundermail

Folders and mail arrive in the account

Begin the transfer. Folder by folder, the converter pushes your Outlook mail up to Thundermail through the IMAP link, and the folder names, message dates and attachments go with it. Once it finishes, sign in to Thundermail and the Outlook folders are there next to your new mail, reachable from any device.

Do My Outlook Folders Come Across?

Yes. The converter rebuilds your Outlook folder layout inside Thundermail, so the Inbox, the Sent folder and every nested or archive folder land under the same names. Dates, read status and attachments ride along with each message. The effect is your Outlook mailbox appearing in Thundermail as it was, not a flat pile you have to sort again.

You also decide what travels. As the PST opens, each folder shows a tick box, so a heavy Deleted Items folder or a stale archive can be left out and only the mail you care about goes up to Thundermail. Whatever you unticked remains in the PST on disk.

The worry with leaving Outlook is always the old mail. Once people see the folder tree land in Thundermail intact, the switch stops feeling risky. The PST carries the structure, and IMAP puts it back on the other side.

Nick Rogers, Founder, Univik

What About Outlook Rules and Settings?

Mail moves, client settings do not. Outlook rules, signatures, categories and account options live in Outlook, not in the mailbox, so they do not travel with the mail into Thundermail. This is true of any service move, not only this one. Plan to set those up again in whatever client you point at Thundermail afterwards.

What does come across is everything that is actually mail: the messages, their folders, dates and attachments. For most people that is the part that matters, and rebuilding a handful of rules in the new setup is a small task next to keeping the archive.

Which Outlook to Thundermail Route?

Three ways to shift Outlook mail across. Only one moves the whole mailbox with its shape kept.

What you need	Drag between accounts	Free online mover	Convert through a PST
Moves the whole mailbox	One at a time	Partly	Yes
Keeps the folder tree	No	Often flattens	Yes
Works without Outlook open	No	Varies	Yes
Mail stays off other servers	Yes	No	Yes
Handles a large archive	Poorly	Poorly	Yes
Good for	A few messages	A small mailbox	A full Outlook move

Take your Outlook mailbox into Thundermail

Point Univik Email Converter at an Outlook PST and your Thundermail account, and it carries the mailbox across over IMAP with the folder tree, dates and attachments in place. Outlook can stay closed. One run moves years of mail into the new service.

⬇️ Download Free Trial See what it moves →

Runs on Windows 7 through 11 · the PST is read with Outlook closed · the trial carries a few messages per folder

The short version

Export Outlook mail to a PST, or use one you already have.
Create a Thundermail app password in the dashboard.
Load the PST in Univik Email Converter and pick the IMAP destination.
Use the Thundermail server on port 993 with SSL/TLS and the app password.
Folders, dates and attachments arrive in Thundermail, no Outlook open needed.

Move Outlook mail to Thundermail, free trial

Outlook to Thundermail Questions

Should I export Outlook to a PST or connect both accounts over IMAP?

Exporting to a PST and uploading it is the reliable route for a full move. Adding your old account and Thundermail side by side in a client and dragging mail can work for a handful of messages, but it is slow and often drops the folder tree on a big mailbox. A PST holds the whole mailbox in one file, and a converter writes it into Thundermail in a single pass with the structure intact.

Do my Outlook contacts and calendar move to Thundermail as well?

This guide moves email. Contacts and calendar entries in Outlook are separate items and are not part of the mail move, so plan those on their own. Thundermail includes calendars and contacts of its own, and you can export the Outlook address book and calendar and bring them in through Thundermail rather than through the email transfer. The mailbox move here covers messages, folders and attachments.

Can I keep using Outlook after moving to Thundermail?

Yes. Moving the mail into Thundermail does not close your Outlook, and you can add the Thundermail account to Outlook over IMAP so both sit in the same window during a changeover. Use the Thundermail server on port 993 with SSL/TLS and an app password to add it. Many people run both for a short while, then drop the old account once the Thundermail move settles.

How do I plan the cutover from Outlook to Thundermail?

Move the mail first, check it landed in Thundermail with its folders, then switch where new mail arrives by updating your address or forwarding. Keeping both accounts live for a short overlap avoids missing anything in transit. Set up Outlook rules, signatures and filters again in your Thundermail client during that window, since those settings do not travel with the mailbox.

Do I need Outlook installed to move the mail to Thundermail?

Not for the upload. You need Outlook only to export the PST if that is where your mail is now. Once you hold the PST, Univik Email Converter reads it on its own and uploads it to Thundermail, so Outlook can be closed or absent for the transfer. If you already have a PST or an OST archive, you can move it without opening Outlook at all.

What if my Outlook archive is very large?

A large Outlook mailbox moves fine, it only takes longer to upload over IMAP. Univik Email Converter reads the PST directly rather than through Outlook, which avoids the profile and size limits Outlook can hit on a big file. You can also break the move up by selecting folders, sending the important mail first and the archives later, so a slow upload does not hold up the switch.

About This Guide

Written for Univik by Leena Taylor Paul, drawing on Univik's long run of Outlook migration work since 2013. The Thundermail server details were checked on its beta support pages during 2026. The Outlook move was tried by sending a PST of nested folders up to a live IMAP mailbox. 23 September 2026. A folder missing after the move? Support is a click below.

Sources: Thundermail IMAP settings guide · What is Thundermail · Univik Email Converter