There's no RFC specifying a limit to the depth of nested compressed files. However, most virus checking programs will only go down to a certain depth when scanning compressed files. It is this program to which he refers when he mentions the error "zip file is too deep". This is to protect the server from being bogged down by intentionally deep files (on the order of thousands deep). There are some programs that treat nested zip files as directories along a path, and have a finite path length, so this depth limit may also be meant to prevent buffer overruns in the path, which can be a security problem in poorly designed compression software. Limiting the depth is a poor solution, though, because an archive could contain a very deep path already, such that zipping it once would break software that places limits on path length. It is certainly ludicrous to change that setting so that files which are compressed twice cause this problem. A more sane setting would be between 5 and 10 deep, which would allow most backups (which often contain zip archives) to go through. Technically, I doubt RFC compliant mail servers care. Generally software plugins for virus and spam detection are used to examine attachments - the mail server has little need to unzip anything. This further removes the whole issue from the realm of RFC compliance. His comments are technically odd, but the message is simple: "I will not support nested compressed files. If you are experiencing problems, you are on your own unless you follow my guidelines." -Adam On Wed, Sep 15, 2010 at 3:14 PM, Vitaliy wrote: > We started having problems with emails getting blocked by one of our > vendor's mail servers: > > : > 123.65.145.12 failed after I sent the message. > Remote host said: 551 Message contains ZIP file that is too deep (4) (Mod= e: > normal) > > The president of their IT company said this: > > "Even though the manufacturer allows it, I would not put a zip archive > inside other zip archives as a standard practice. The path to the archive= d > file can be too long, thus the message that the "zip file is too deep". > > Just to let you know, it is also a standard virus ploy (hiding infected > files or malware inside a clean archive) that is no longer allowed by man= y > RFC-compliant mail servers. " > > I did a search out of curiosity, but could not find the RFC in question. = Is > he full of it? > > Vitaliy > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://chiphacker.com/ - EE Q&A site --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .