I use my droplet as email server based in Nethserver from a few years.
Now my emails are rejected and I receive this message.
Could you help me?

Best regards

This is the mail system at host nethserver.secuware.com.

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

<xxxx@hotmail.com>: host
   hotmail-com.olc.protection.outlook.com[104.47.22.161] said: 550 5.7.1
   Unfortunately, messages from [207.154.196.78] weren't sent. Please contact
   your Internet service provider since part of their network is on our block
   list (S3150). You can also refer your provider to
   http://mail.live.com/mail/troubleshooting.aspx#errors.
   [DB8EUR06FT041.eop-eur06.prod.protection.outlook.com] (in reply to MAIL
   FROM command)
Reporting-MTA: dns; nethserver.xxxx.com
X-Postfix-Queue-ID: C5F3142355
X-Postfix-Sender: rfc822; xxxx@xxxx.com
Arrival-Date: Fri, 29 May 2020 21:07:16 +0200 (CEST)

Final-Recipient: rfc822; xxxx@hotmail.com
Original-Recipient: rfc822;xxxx@hotmail.com
Action: failed
Status: 5.7.1
Remote-MTA: dns; hotmail-com.olc.protection.outlook.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [207.154.196.78]
   weren't sent. Please contact your Internet service provider since part of
   their network is on our block list (S3150). You can also refer your
   provider to http://mail.live.com/mail/troubleshooting.aspx#errors.
   [DB8EUR06FT041.eop-eur06.prod.protection.outlook.com]
edited by MattIPv4

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1 answer

Same issue here.
Looks like outlook.com are blocking digitalocean ip’s
Were you able to fix this?

  • No. It seems that Gmail consider that the IP of DigitalOcean reputation went from Normal to Pesime in May 12th.
    Use https://postmaster.google.com/ tools to verify what think Gmail about your IP, domain, etc

    We move our email server to Amazon Web Services to get a fresh IP. Gmail says that the reputation of the IP of our droplet is influenced for the reputation of other IP in the same range. So, If somebody uses a droplet in DigitalOcean to spam, this guy affects to reputation of all IP.

    If you decided to move to AWS as we did, you have to ask permission from AWS in order to open the 25 port (SMTP).

    I hope our painful experience (1 month with all our emails marked as spam in Gmail and Hotmail) help you.

    You can use this great tool too to verify status of your email server:
    https://mxtoolbox.com/domain/

    Implement DKIM, SPF and DMARC to increase reputation.

    Have luck.
    Best regards

    • Actually this can happen with any web hosting provider. I’ve had the same issue with both managed and unmanaged hosting providers.

      Regarding AWS blocking port 25, DigitalOcean actually have the same approach, port 25 is closed for all new accounts.

      The email header that you’ve shared is referring that it is a hotmail issue. To be honest, hotmail’s new email filter are really not working and they’ve been catching a lot of false positives than they should.

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