If you’ve been using Thunderbird to manage your email account, or have simply used it to back up a hosted email account then you can connect Thunderbird to a Gmail account and upload all existing emails there. This is quite straightforward to do, but can take a lot of time if you have hundreds and thousands of emails to transfer.
1. Enable IMAP access in your Gmail account
Go to Account -> Settings (use the top right icon to access this)
Go to the Forwarding and POP/IMAP Tab
Under IMAP access make sure you have checked ‘Enable IMAP access’
Save the changes
2. Enable Access for less secure apps (temporarily)
Under your gmail avatar icon at the top right you will find your general Google Account Settings
Go to the Sign-In & Security section on the left of the screen and find the ‘Apps with account access’ link
In the bottom section of that page enable ‘Allow less secure apps’
You will receive an email notification from Google warning you that this setting has been modified. We will be disabling this again once our email import has been completed.
Now you’re ready to configure Thunderbird to sync with your Gmail account.
3. Set up Gmail as an IMAP account in Thunderbird
Select Tools -> Account Settings
At the bottom of the screen you will see a dropdown list of Account Actions where you can click ‘Add Mail Account’
Type your name and gmail email address
Thunderbird will now attempt to retrieve the configuration settings. If the values are correct then use Done to finish this step. Otherwise use the Manual Config button to edit the values until they are correct.
You now need to authenticate Thunderbird with Gmail
Thunderbird will now try and connect to your gmail account
It will take a few minutes to sync, but then you will see the list of Gmail folders appear in Thunderbird
You can disable checking for emails as we’re only looking to import into the Gmail account. Do this by going to the Gmail account in Thunderbird and choosing the Server Settings section.
4. Import Email from Thunderbird to Gmail
This is a simple drag and drop process in Thunderbird from your original email account to the gmail account.
In Thunderbird select a folder you want to import to Gmail
Drag and drop that folder into the Gmail account to upload the folder and messages to Gmail
If you look in your Gmail online account you will see a label has appeared for that folder and the messages are in it. The conversations will be nested like they usually are in Gmail.
Repeat this for all folders you want to copy. Some folders will take a lot of time to upload into your Gmail account. You can see the status at the very bottom of the Thunderbird pane.
If you don’t want to upload an entire folder you can select specific emails and drag them into the Gmail folder where you want to store them.
Command and A will select all emails in a folder for copying. Note that the connection may time out if you are transferring a lot of emails in one go and you will need to repeat the transfer to make sure you get them all.
Import Inbox and Sent Mail
Don’t forget to copy over emails in your Inbox and Sent Items folders into the Gmail Inbox and Sent Mail folders. Select the emails you want to copy and then go to Message -> Copy To… or just right-click the selected messages and select Copy To
In this example I copied the Inbox items to a Gmail label called firstname.lastname@example.org to keep the archived emails separate to the current Gmail Inbox. You may need to copy these in batches as a large number of emails may not transfer successfully in one go.
Here I am copying the Sent Items into the Gmail Sent Mail Folder
5. Final Steps
The last step is to disable access for less secure apps in your Gmail account again. Repeat the steps from the “Enable Access for less secure Apps” step above, only this time disable access.
Now you should have all your email available within your Gmail account.