Why are some file types are blocked to be attached in email in Gmail?

For G Suite.

For Office 365.

Question:

Why are some file types are blocked to be attached in email in Gmail?

Answer:

If the receiver is using Gmail, there are restrictions on file types for sending and receiving.

If you attach the types of files listed in the reference, you will have restrictions on what you can send and receive, so please note that.

- Extract from reference
It isn't possible to send a password-protected zip file containing a zip file.
Please de-compress all files or remove the password protection if possible.

Furthermore, while you activate "ZIP encryption function" in our service, if you attach a file ending in ".zip", it becomes "doubled ZIP"(*), and it may be restricted by Gmail.

*A password-protected zip file containing a zip file.

To avoid such a situation…

  1. Announce users not to attach ZIP files, and activate ZIP encryption function.
    (*Default setting)
    (Security level: High, User load: Low ) 


    Merit
    Encrypt all files automatically and uniformly.

    Demerit
    If a user attaches ZIP file, it will be a doubled ZIP file. So, you need to announce users thoroughly not to attach ZIP file which was created in PC environment or etc.

  2. In the case ZIP file is attached, system will delete it.
    (Security level: High, User load: Middle)

    Merit
    Users can attach the file they would like to send as it is. Users thoroughly use random passwords given by the system, and thus this operation doesn’t allow users to create ZIP files.

    Demerit
    If ZIP file is attached, the e-mail will be deleted. So sender has to send it again with the attached file in another format.
  3. If ZIP file is attached, system doesn’t make it ZIP encrypted.
    (Security level: Middle, User load: Low)

    Merit
    Operation which admits attaching ZIP files, and avoids only doubled ZIP status.

    Demerit
    Operation which tolerates sending unencrypted ZIP files to receivers.

If you have a desired setting, we will change the settings. Please contact our support team.

          
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