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How Apple Mail hit Finder copy error -36 when saving attachments and the dot_clean + rsync workaround that recovered all files

December 5, 2025

In today’s digital ecosystem, macOS users often rely on native applications like Apple Mail and Finder for daily workflows — from handling emails to organizing and transferring files. While usually seamless, this integration can occasionally produce puzzling and disruptive technical errors. One such example is the infamous Finder error code -36, which can unexpectedly appear when saving attachments from Apple Mail. Though the error might sound cryptic, it typically relates to file transfer issues rooted in certain metadata discrepancies. This article explores the causes of this error and outlines a reliable, field-tested workaround using dot_clean and rsync to recover files without data loss.

Table of Contents

TL;DR

Apple Mail and Finder users sometimes encounter the -36 error when attempting to save email attachments to a local or external volume. This error usually stems from hidden metadata conflicts, especially when transferring files to non-HFS+ or non-APFS formatted drives. By combining the use of dot_clean and rsync, users can recover and copy files cleanly without triggering the Finder error. This method is particularly effective in resolving invisible file issues that interrupt standard copying operations.

Understanding the Finder -36 Error

The -36 error is a legacy Mac OS error that typically reads: “The Finder can’t complete the operation because some data in [filename] can’t be read or written. (Error code -36)”. The error is known for being vague and notoriously difficult to trace. However, over the years, user reports and filesystem-level inspection have revealed that it often points to issues with hidden .DS_Store files or ._ AppleDouble resource fork files, particularly when interfacing with non-native storage formats like FAT32 or exFAT.

In practice, users attempting to download and save attachments from Apple Mail directly to such drives may encounter the error, halting the copy process and in some cases, preventing access to the save destination altogether.

How the Issue Was Detected

In one reported instance, a macOS Ventura user was saving multiple PDF and image attachments from Apple Mail to an external SSD formatted in FAT32. The copy operation began normally, but stopped midway with the -36 error. Attempts to retry the operation failed at different points, suggesting file-specific or metadata-related sensitivity.

[p]What made this incident particularly concerning was that the attachments weren’t recognized as corrupted or active files elsewhere. They were inspectable and previewed correctly in Apple Mail, yet became problematic when exported through Finder. Traditional diagnostics failed to offer insight, pushing the need for terminal-level investigation.

Why dot_clean and rsync Work

After a series of tests, the issue was diagnosed as one involving hidden Apple metadata files. When Apple Mail saves a file onto a volume not natively supporting HFS+ metadata, it uses AppleDouble format to store this extra data — generating files prefixed with ._. These hidden files often confuse or conflict with foreign file systems, leading to the -36 error.

This is where dot_clean and rsync come into play:

dot_clean — This command merges ._ files with their associated parent files, or deletes the redundant resource forks if incompatible.
rsync — This tool allows robust file copying with logic that can skip problematic metadata, preserve integrity, and retry failed copies.

As a combination, these tools provide a safer, deeper way to recover and copy files than Finder’s drag-and-drop interface can offer.

Step-by-Step Recovery Using dot_clean and rsync

Below is a battle-tested process that helped recover over 400 email attachments without triggering Finder error -36:

Open Terminal: Launch the Terminal application found in /Applications/Utilities.
Navigate to the directory where attachments have been downloaded. For example:
```
cd /Users/yourname/Downloads/MailAttachments
```
Use dot_clean on the folder to merge or remove AppleDouble files:
```
dot_clean .
```
This helps sanitize the folder before copying.
Use rsync to transfer the files to the external volume or another location:
```
rsync -avhE . /Volumes/YourDrive/RecoveredAttachments/
```
The -E flag attempts to preserve extended attributes and resource forks.

Once executed, the files were transferred successfully, bypassing any -36 Finder errors and retaining full file integrity.

Why Finder Fails While Terminal Succeeds

Finder is designed for user-friendly file operations but does not offer granular handling of hidden metadata files. It treats files and resource forks as separate entities, and when these forks are incompatible or inaccessible, Finder halts the operation with generic messaging.

In contrast, terminal tools like rsync allow for more flexible logic. rsync can preserve or omit extended attributes as required and is more tolerant of system inconsistencies during transfers. dot_clean proactively eliminates cause for conflict by tidying up legacy Apple file forks or DS_Store conflicts that Finder fails to resolve.

Implications For Enterprise and Creative Professionals

For users relying heavily on email attachments for legal, media, or corporate correspondence, encountering sudden copy errors can mean hours of wasted effort and uncertainty. In team environments where SSDs or shared volumes are formatted with cross-platform compatibility in mind (such as FAT32 or exFAT), this error is increasingly relevant.

Creative professionals especially — who move bulk design mockups, photos, or PDFs — must remain vigilant of how Apple’s metadata interacts with foreign filesystems. Knowing how to apply dot_clean and rsync is a vital troubleshooting skill in such environments.

Preventing Future Issues

To avoid encountering Finder error -36 when saving attachments in the future, consider these practices:

Avoid saving directly from Mail to external volumes formatted in FAT32 or exFAT. Instead, save files locally and move them later after cleaning metadata.
Use HFS+ or APFS formatting when selecting drives for primary use with macOS systems.
Run dot_clean periodically on shared folders, especially if you notice performance or file access issues.
Familiarize yourself with key terminal commands like rsync, cp -R, or even ditto, which offer more recovery potential than GUI methods.

Conclusion

The Finder -36 error is a frustrating but fixable problem. By understanding the root cause — hidden Apple metadata clashing with external volumes — and applying robust command-line utilities like dot_clean and rsync, users can confidently navigate around this glitch. At a time when data loss can have far-reaching consequences, having a reliable method for file recovery is essential knowledge for every serious Mac user.

As macOS continues to evolve and third-party compatibility becomes more complex, errors like these remind us of the importance of technical agility. Being prepared with reliable tools and procedures can make all the difference between a failed operation and a recovered workflow.