a critical warning for all apple mail users: the export data-loss bug
exporting your emails from apple mail to a standard mbox file seems like a safe and straightforward way to create a backup or migrate to a new system. apple's own documentation presents it as a simple, reliable process. however, lurking within this function is a catastrophic, undocumented bug that can lead to silent data corruption and permanent loss of your valuable emails. this bug is a hidden file size limit: if your mailbox is larger than approximately 2.15gb, apple mail may silently truncate the export, cutting it off mid-email without providing any warning or error message. you are left with a corrupt, incomplete mbox file and a false sense of security that your backup is complete.
this article will first show you the "official" way to export your mailboxes and then explain in detail how to protect yourself from this critical flaw.
the "official" method for exporting a mailbox
on the surface, the process is very simple. to export a single mailbox (e.g., your inbox or a specific project folder) from apple mail, you follow these steps:
- in apple mail, select the mailbox you want to export from the sidebar on the left.
- from the menu bar at the top of the screen, click on mailbox.
- from the dropdown menu, select export mailbox...
- choose a location on your mac to save the file, and click choose.
apple mail will then create an `.mbox` package. inside this folder, you will find a file named `mbox`, which is the actual archive file containing your emails. for a small mailbox, this process works perfectly. the danger arises when you try to export a large mailbox that has accumulated years of messages and attachments.
the hidden 2.15gb time bomb
multiple independent sources and frustrated users in forums have confirmed this dangerous limitation. one user painfully recounts: "apple mail has a size restriction of 2.15gb where it just cuts off!!!... so i had to split my apple mail archive into 30 or so folders and export... them one by one." another technical guide explicitly warns: "note: apple mail can only export inboxes up to 2.15gb."
the most sinister part of this bug is its silence. the export process will appear to complete successfully. there is no warning, no error dialog, nothing to indicate that the resulting file is a corrupted, incomplete version of your archive. if you then delete the original emails from apple mail, assuming your backup is safe, you could be facing irreversible data loss.
warning: do not export any apple mail mailbox over 2gb. the app may cut your file off without warning, leading to a corrupt mbox and permanent data loss.
the mandatory step: verify every export
given this critical flaw, you can no longer trust apple mail's export function blindly. every single export you perform must be immediately verified to ensure its integrity and completeness, especially before you rely on it as a primary backup. how do you verify a multi-gigabyte text file? you don't do it manually. you use a reliable tool that can quickly open and inspect the file.
this is where the mbox viewer chrome extension becomes an essential part of a safe backup workflow. because it can handle very large files and is not subject to the same bugs as apple mail, it is the perfect verification tool.
your new, safe exporting workflow must be:
- follow the steps to export your mailbox from apple mail.
- immediately locate the exported `mbox` file.
- drag and drop the file directly into the mbox viewer.
- quickly scroll to the bottom of the email list. check if the oldest emails you expect to be there are present. perform a search for a key term from an old email.
- only once you have verified that the export is complete and all emails are accounted for should you consider the backup to be safe.
by treating every apple mail export as potentially corrupt until proven otherwise, you protect yourself from a devastating bug. don't let a silent flaw in the software jeopardize your data. export, but always, always verify.