Mozilla Thunderbird
A desktop mail client with email accounts, calendars, address books and extensions, with local cache and migration workflows for IMAP or POP accounts.
What Thunderbird does
Thunderbird brings multiple IMAP or POP accounts, calendars, contacts and extensions into a desktop workspace. Server policy, synchronization scope, local cache and attachment handling are separate concerns, so account setup and profile backup should be planned together.
Local data and migration
Offline synchronization and cache settings determine which messages and attachments are stored on a device. Before moving to another computer, close the client, back up the profile and verify accounts, folders, contacts and calendars in stages. A copied profile is useful evidence, but a migration is complete only after send, receive and restore checks pass.
Maintenance note
This page reviews Mozilla Thunderbird 153.0.1 for macOS, account authentication, IMAP and SMTP synchronization, attachment cache, extensions and profile migration. Content review date: 2026-08-23.
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Mozilla Thunderbird 153.0.1 macOS installation and mail setup guide
Install the app and make a profile backup, add one low-risk test mailbox, verify sending, receiving, synchronization, calendar and contacts, then migrate other accounts.
Before you start
- Confirm the macOS universal package and reserve space for message cache, attachments and backups.
- Prepare the mailbox address, authorization or app password, and IMAP and SMTP server settings.
- Close the previous mail client and keep a rollback copy of the profile, contacts and important messages.
Installation steps
- 01
Install the 153.0.1 universal package
Open the disk image, move Thunderbird into Applications and verify the version and update settings after first launch.
- 02
Add a test mailbox
Add a low-risk account first, confirm automatic IMAP and SMTP parameters, authentication and folder subscription, then test send and receive.
- 03
Configure calendar, contacts and extensions
Enable services as needed, install extensions one at a time and inspect permissions, attachment directory and local-cache behavior.
Quick start
- 01
Verify mail and synchronization
Send, reply and move a test message, compare desktop and web status and test a large attachment separately.
- 02
Protect local profile data
Use macOS account and lock-screen protection, limit offline downloads on shared computers and back up the profile to a separate location.
- 03
Migrate other accounts
Add additional mailboxes one at a time, recording sync scope, signatures and filters so each account can be isolated during troubleshooting.
Usage tips
- IMAP, POP, offline cache and server retention produce different deletion results; check which devices are affected before removing mail.
- Mail extensions, calendar connectors and attachment handlers can read local or network content, so install only reviewed items.
- Verify that a backup can be restored instead of treating a directory copy as a finished migration.
Troubleshooting and uninstall
Why does account authentication keep failing?
Check address, app password, IMAP or SMTP port and encryption mode, then review the provider's extra authorization requirements without repeatedly guessing passwords.
Why are folders or attachments missing?
Check folder subscriptions, offline scope, disk space and server attachment limits, then synchronize one folder before expanding the range.
- Export and back up account dataClose Thunderbird, back up profile, contacts, calendars and important messages, and verify the recovery copy opens.
- Sign out and clean local dataRemove local accounts or sign out, confirm server-side mail remains accessible, then uninstall and clear cache or attachments as required.
Frequently asked questions
Can Thunderbird manage multiple mailboxes?
Yes. It can group multiple IMAP or POP accounts in one desktop workspace, while each provider still controls authentication, folders and retention.
Are messages automatically stored locally?
Local storage depends on account type, offline synchronization and cache settings. Shared devices should use account protection and a deliberate offline range.
What should be backed up before migrating?
Keep the profile, account settings, contacts, calendars and important messages, then verify a staged restore before removing the old copy.