Forwarded message blocked by gmail

Hi there

I have been attempting to debug this problem for the past few days without much luck.

My situation is as follows: I can reliably send and receive email to and from my mailinabox email server. But when I set up an email forward in roundcube, the message is blocked by gmail with the following message:

This is the mail system at host

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

               The mail system host[2a00:1450:400c:c07::1b]
said: 550-5.7.1 [2a01:4f8:c17:6e4b::2 12] Our system has detected that
this 550-5.7.1 message is likely unsolicited mail. To reduce the amount of
spam sent 550-5.7.1 to Gmail, this message has been blocked. Please visit
550-5.7.1 550
5.7.1 for more information. d6si7488468wmf.127 - gsmtp (in reply to end of
DATA command)

I just don’t know what I’m doing wrong here. I recently moved all the email onto a new mailinabox instance on a new server with new IP. All status checks and mail-tests pass.

Can anyone suggest any approaches to debugging this issue?

It may be something else, but I did notice that when moving an email to a new server/IP, gmail flag them as spam for a few weeks.
What empirically help :

  • registering your domain on (even if traffic is too low to get stats)
  • having gmail user flag mail as not-spam if/when they receive them.
  • sending a couple email a day to and from the concerned adress from several valid gmail accounts for a week or two. (only one recipient per mail)

Same with office 365 / outlook , actually . ( , iirc). In that case, there is a form you can fill to certify that “I am not a spammer, please unban me.”

Hope this can help.

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