search for: save_is_attachment

...mail_attachment_min_size = 128k It's also possible to create a plugin that adds further restrictions to when the attachment is saved separately. This might be useful to reduce disk seeks for attachments that are typically shown inline by clients/webmail. You can do this by overriding mailbox.save_is_attachment() method. If you want to distribute attachments to multiple filesystems, just create /var/attachments/[0-9a-f][0-9a-f] as symlinks pointing to whatever mount paths you want.