By comparing the mails sent by standard clients such as OutlookExpress and Webmail, we can find ten important features of spam:
(1) does not have an X-Mailer letterhead, or a special X-Mailer letterhead is used. We see that there is an X-mailer in the email header sent Out-Look: Microsoft out-look IMO, build 9.0.2416 (9.0.2910.0). However, spam either has no or a characteristic header, such as x-mailer: ehoosend.
(2) Forge the sender. The MailFrom in the MTP command is inconsistent with the From in the mail body, and the email address of the sender is not the real email address.
(3) Send through dynamic IP such as ADSL. External users directly connect to MX server through dynamic IP, but SMTP service is not provided locally, so IP cannot be interpreted reversely.
Extended data:
Main danger
(1) occupies a lot of network bandwidth, wastes storage space, affects network transmission and operation speed, causes mail server congestion, reduces network operation efficiency, and seriously affects normal mail service.
(2) The flood of mail in wheelie bins doubles every five months, and foreign experts estimate that the productivity cost offset by each spam is about $65,438 +0. China has been regarded as a hotbed of spam by other countries, and many IP addresses are in danger of being blocked, which may make China an "information island" for a long time.
(3) Spam is characterized by its large quantity, repetition, compulsion, deception, unhealthy and fast spread, which seriously interferes with the normal life of users, infringes on the privacy and mailbox space of recipients, and consumes the time, energy and money of recipients.
(4) Spam is easy to be used by hackers, which is more harmful. In February 2002, hackers first invaded and controlled some high-bandwidth websites, concentrated the bandwidth capacity of several servers, and then launched a fierce attack with hundreds of millions of spam messages, resulting in the paralysis of some websites.
Reference source: Baidu Encyclopedia-Spam