Why does the filename sometimes show up as [Auto_Compressed.zip] on the recipient side?

for Google Workspace / Microsoft 365

Question

For ZIP Encryption feature, why does the filename sometimes show up as [Auto_Compressed.zip] on the recipient side?

Answer

If the filename exceeds 255 bytes after being encoded, the filename will be compressed and automatically turned into [Auto_Compressed.zip].

**Note that similar to the email body, the attachment filename will also be encoded. The specification may differ depending on the encoding system. For Japanese, the rough estimate is that around up to 60-70 characters are allowed without being auto-compressed.