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Re: puzzling junk mail




Tanstaafl wrote:
On 2/8/2019, 12:34:31 AM, Daniel <dxmm@xxxxxxxxxxxxxxxxxxxxx> wrote:
as some servers do apparently require a To: addressee,

Never seen one that did.

SMTP doesn't distinguish To Cc or Bcc, only RCPT-TO.


SMTP doesn't, but some servers (e.g. filtering tools used by the server's Mail Transport Agent) may reject messages that don't have To: or cc: addresses. That's a decision that's made, based on content scanning of the message content.

I know that there are also some servers that may reject (or at least tempfail) envelopes with more than a specified number of addresses in the envelope. Last I recall, Yahoo's threshold was 10 addresses.

I know of a longtime spam operation that uses addresses harvested from victims, where they send to portions of the victim's address book, and where all the addresses are To: (and display names shown in alphabetic order). For this, one of the hooks is that addressees are likely to be known to each other (as well as to the name associated with the forged sender address). One of the trademarks of this operation is that content always goes out in increments of about 10 at a time (give or take), and my assumption has always been that the relatively short distribution list is done as a way of getting stuff past servers that limit the number of addresses in an envelope.

Smith
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