CLEMENT Francis wrote: >I had the same problem when using symantec av smtp gateway and some = >clients >too with some avs ... > >First, note that a pure mta have nothing to do with the message itself >(expect to add its own Received from, etc, in the header part) and have = >not >to control it. The pure mta actes on tcp/ip smtp session data only (and = >have >to control it with rfc rules). > >AV gateways are like xmail + filters, a mta and content filters. > >So now, at filter stage : >The headers part of the message can't contain a null, as any line in = >the >headers part have very strict writing rules in the rfc's : only subset = >of >printable chars from 32-127 and cr/lf. > >Then after the empty line, begins the message body. >The problem is how filters programmers read the rfc and how they class = >a >null char : > >"The mail data may contain any of the 128 ASCII characters. All = >characters >are to be delivered to the recipient's mailbox including format = >effectors >and other control characters." > >"128 ASCII characters" : strictly reading is it 'From 0 to 127', so a = >null >byte in the mail is ok. > >Some don't classify the 'null byte' in the 'characters class' nor the >'control characters class' : then null byte is not ok. > >And another point to verify in rfcs, assuming 'a null byte' is a ASCII = >char >(yes it is ...): >Don't know exactly if MIME RFC's says anything about null and others = >control >caracters, but 'in mind' in a MIME formatted message, any 'special' >character (not in range 32-126) need to be encoded, so a null byte have = >to >be encoded, then finaly a MIME formatted message can't contain a 'pure' = >null >byte in the data ... >If you don't create a MIME message (only plain text from 0-127 char = >set, no >mime headers, no possibility for attachements and multiple formats in = >same >mail, ...), you can have 'pure' null bytes in the data,=20 >but if creating a MIME message you can't. >The AV problem can then simply be a bug if the mail in not a mime = >message >.... but the filter don't check and allways assume a Mime message. > >Francis > > Even if you classify a null byte as "not ok", only a lobotomy should excuse someone from just letting an AV scanner, spam filter, what have you, hang when encountering one. I can't for the life of me figure out why Mcafee or Symantec (and others?) won't address this issue.
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