Why are emails that has recipients of less than 10 external domains get discarded?

For G Suite.

For Office 365.

Question:

One of Email Security's Default rules stated that email that has recipients of 10 or more external domains will be discarded automatically. Why are emails that has recipients of less than 10 external domains get discarded?

Answer:

In case of setting the filter to limit the number of the mail addresses /phone numbers appearing in the text, it requires some settings such as;

“If there are XX or more of **(target text string ) in the text, the mail should be deleted and the sender needs to be notified about it. ”

But, there are some cases that the mail is judged to be a target of deletion even if the addresses and phone numbers are fewer than the designated number. This occurs when the mail is created in the [rich text format].

When creating the mail in [rich text format], the mail text will be generated in the [multipart format].

In Multipart Format;

  • The mailer compatible with HTML mails displays the mail in HTML format.
  • The mailer incompatible with HTML mails displays the mail in Plain text format.

Therefore, in the mail created in [multipart format], both of the plain text format data and the HTML format data are contained in the mail text.

From the reason above, for the mail created in [rich text format], the actual number of the characters contained in the mail text should become twice as many as that of the displayed characters.

i.e.;
In the mail created in [rich-text format], the number of text strings designated by the filter condition should be 2 times greater than that of the actually contained string text.

Furthermore, if the part of the conditioned text string is to be the link form, it increases the number of the text strings contained in the HTML form so that it will be counted 3 times as many.

When often creating the rich text format mail, the above details should be considered to set up the value.

          
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