How can I configure Thunderbird to prevent it from automatically deleting messages from its local mailbox when they're deleted on the server?

Question

I've got a scenario where I need to retain a backup of an IMAP email account in Thunderbird when it even has email deleted from it on the server. In other words, I just always want it to keep accumulating all email forever and if I delete it from another mail client, it should just remain in this one in Thunderbird.

It seems like there should be a setting somewhere in the advanced "about:config" area having to do with expunge or something similar that would allow local deletion policy to be disabled, but I've had no luck finding it so far.

I also thought perhaps there might be some setting like "Do not delete any messages" under the Server Settings for the IMAP account or perhaps in its Advanced... button settings dialogue, but there's no such option that I can find.

Any idea on how to accomplish this?

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CONTEXT:

Just to clarify the context of this situation: Dealing with a friend who's recently had a loved one who had a stroke which has affected many aspects of their ability to reason/recall, but unfortunately they still give the appearance of being able to function somewhat normally and have reasonably good long term recall. This has lead to their accidentally and repeatedly deleting all of their email history for the past 25 years. This is very bad and the individual themselves doing this action on their shared family email is also upset (each time it has happened) about doing this.

The goal is to create an easy access client email reader backup that the other family members can still use and retain a copy of everything conveniently even in the face of incessant inadvertent deletion by their loved one.

Currently the restorative process with the host is becoming quite costly since the host has a fee each time for the restoration process. They also only serve IMAP (they apparently phased out POP3 service several years ago).

The companion who primarily uses the email is also elderly and needs a very, very simple client option - Thunderbird is the best I could think of, but I could get them to spring for Outlook too probably, they're just being "nickeled and dimed" to death presently with the situation.

Answer 1

It's my understanding the nature of IMAP is that you are looking at a remote view of your mail and it's not technically sitting on your hard drive, although it's cached in a file, I don't know if any way to prevent deleting other than using the archiving feature which might serve your purpose. You can set Thunderbird's auto-archiving feature to archive mail into a folder that sits on your hard drive instead of archiving it on the IMAP server.

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Additions Releted to Context

In the case of your context set up the owner with a mail client using the POP protocol, instead of IMAP. Setting the option to not delete mail from the server in the settings will make sure that any mail deleted will only happen on the local side.

Another option is to use a Mail Archiving Client like MailStore MailStore Home is free for personal use (Up to Three Email Accounts). Then the family that wants to retain access to the email can keep a searchable archive of the mail offline regardless of what is done online. You would have to be sure you could set the client to auto-archive regularly to avoid mail being lost in a delete operation.

Answer 2

As trinsic said, it is the design of most IMAP clients to let the server be authoritative for mailbox contents, so they usually do not have such options.

To make an archive if you're worried about someone deleting messages, you should use a dedicated program, such as getmail or fetchmail or OfflineIMAP or imapsync.

The first two use IMAP in a POP-like manner, retrieving messages from the 'INBOX' into the local archive. (Though if your server supports actual POP, then mpop is another easier-to-configure option.) The latter two perform full synchronization and can be combined with something like zip/rar/7z to keep e.g. monthly archives of the local folder.

Finally, if the server is your own, often it is possible to retain a server-side copy instead, e.g. archiving a copy of all messages as they're delivered into the 'INBOX' (which could be done using existing filtering systems like Procmail that many mail servers already have available), or forcing messages to be moved to a 'Trash' folder when a client tries to expunge them.

Answer 3

Tetsujin:

See if the mailserver also does POP3. This defaults to the behaviour you require. You become the master repository, not the mail-server. –

It might be possible to have Thunderbird move all content into a locally stored folder or "inbox", not tried that so cannot advice.
At work I have to use Outlook, as that is the only option. There I have this in practical use: All email that arrives gets moved into folders - manually, stored in local .PST -files.

Personal preference, here, to have control;

• Always avoid IMAP unless you have reason to stay on it.
• For every subject; Keep emails regarding it in a specially created subfolder (e.g. in inbox).
• Move emails that (for some reason) doesn't comply to this, into that folder.
• Make Thunderbird keep copies of sent emails together with those you reply on
  (Edit > Account Settings > Copies & Folders)
• Always Reply, Reply to all or Forward for emails on the subject.

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With a POP3-account, the content is stored in mbox files in $HOME/.thunderbird/ - if reinstalling or moving is required, create a backup of the content listed by

$ cd $HOME/.thunderbird/ && ls -lA && echo "---" && du -sh *

To get the content back in a new Thunderbird,

• Start the new Thunderbird,
• Create a dummy account,
• Exit Thunderbird - and do:
• cd $HOME/.thunderbird/ - to be safe!
• Delete all content; rm -rf .
• Restore your backup; cp <backup>/.thunderbird/* .
• Restart Thunderbird - you should see your original content.

Answer 4

Unfortunately, as explained in other answers, this is not easily possible due to protocol limitations.

Your best bet is Thunderbird's offline mode, which downloads all messages and stores them offline on your local disk. You will need to do this regularly.

1. Verify that the folder(s) you're interested are selected for offline mode. Right click a folder -> Properties -> Synchronization -> Select this folder for offline use. This is the default state for all folders except Spam and Trash.
2. Click the wireless icon in the bottom left corner of the application.
3. Wait for Thunderbird to download your entire inbox. This may take a significant amount of time and space - Thunderbird downloads the entire message contents along with attachments.
4. Backup the Thunderbird profile to a safe location. Look up where the profile is stored on your platform (on Windows it is under %APPDATA%\Thunderbird\Profiles). The total size of the directory you've backed up should roughly match the size of your inbox - make sure to verify that.