SMTP error from remote mail server after end of data: security issue

hi good day

in my office - i send mails each day - lots of mails. But some of my mailing partners do not get the mails _ in fact - all of them are google-mail-user.

so in other words: all those who use google-mail do not get my mails

i get a response:

This message was created automatically by the SMTP relay on mail.mail-server....
A message that you sent could not be delivered to all of its recipients.
The following address(es) failed: 
    host []
    SMTP error from remote mail server after end of data:
    552-5.7.0 This message was blocked because its content presents a potential
    552-5.7.0 security issue. Please visit
    552-5.7.0 to review our
    552 5.7.0 message content and attachment content guidelines. o3-20020a170906974300b444400715867844445653

well what happened here !? What can i do here!?

Stop sending spam and/or viruses?

Did you read their page in the provided link? Google Mail Blocking Explanation

Depending on your mail app and editor, things like fancy background images or stationary, attachments in signatures, etc. could include a file with one of the blocked types.

1 Like

Who’d do something like that? :joy:


How are you sending those mails?

Maybe you just need to mark the “Server requires authentication” checkbox on SMTP server configuration in your email client.

Edit: Same as @MrToddarama posted.

A long time ago, I wrote a game in C++. The name of the file was 357.exe To send it to a friend who wanted to play the game, I would attach the file to the email as 357.djb and send it. Once received, change the name back to 357.exe and you are good to go.