Google is doing an „awesome“ job with their Mailing-Service… and of course also forces people to open up an account, when setting up an Android phone (should be illegal).
Running WebServers is hard, but running MailServers seems to be like RocketScience… another reason people use WhatsApp and Facebook so much… because those systems managed to stay SPAM free (almost).
EMail is a very broken system. But is still in use… because it has become a „standard“ – just as Microsoft.
I wonder what my next Google-Mail-Server-Error-Message will be…
I can happily receive mails from Google Accounts… but as soon as i want to reply i get stuff like:
   SMTP error from remote mail server after end of data:
    host [2607:f8b0:400d:c03::1a]:
    550-5.7.1 [MyIP6Address] Our system has detected an unusual rate
    550-5.7.1 of unsolicited mail originating from your IP address. To protect our
    550-5.7.1 users from spam, mail sent from your IP address has been blocked.
    550-5.7.1 Please visit
    550-5.7.1 to review our
    550 5.7.1 Bulk Email Senders Guidelines. u66si15473913qki.107 - gsmtp
I am pretty shure my server is NOT hacked and yes i send a lot of mails 😀
Last time it was a different error…
    SMTP error from remote mail server after end of data:
    host [2607:f8b0:4001:c16::1b]:
    550-5.7.1 [MyIP6Address] Our system has detected that this message does 550-5.7.1 not meet IPv6 sending guidelines regarding PTR records and 550-5.7.1 authentication. Please review 550-5.7.1 for more information 550 5.7.1 . x102si19099743ioi.169 - gsmtp
Authentication & Identification

Why is it important to authenticate your messages?

Authentication ensures that your messages can be correctly classified. Emails that lack authentication are likely to be rejected or placed in the spam folder, given the high likelihood that they are forged messages used for phishing scams.

In addition, unauthenticated emails with attachments may be outrightly rejected, for security reasons.

To ensure that Gmail can identify you:

  • Use a consistent IP address to send bulk mail.
  • Keep valid reverse DNS records for the IP address(es) from which you send mail, pointing to your domain.
  • Use the same address in the ‚From:‘ header on every bulk mail you send.

We also recommend the following:

  • Sign messages with DKIM. We do not authenticate messages signed with keys using fewer than 1024 bits.
  • Publish an SPF record.
  • Publish a DMARC policy.

Learn more about email authentication.

Additional guidelines for IPv6

  • The sending IP must have a PTR record (i.e., a reverse DNS of the sending IP) and it should match the IP obtained via the forward DNS resolution of the hostname specified in the PTR record. Otherwise, mail will be marked as spam or possibly rejected.
  • The sending domain should pass either SPF check or DKIM check. Otherwise, mail might be marked as spam.

so let’s see how far we get with this

Add & verify your Authentication Domains
What’s an Authentication Domain?

An authentication domain is either the DKIM (d=) or SPF domain (Return-Path domain) that is used to authenticate your email. You can find it in the ‘Authentication Results’ header of an email that has successfully passed authentication (and was delivered to a Gmail mailbox).

For example, in the sample Authentication Results header below, is the ‚Authentication Domain.‘:

spf=pass ( domain of designates as permitted sender)
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; s=12345;;

Postmaster Tools uses your authentication domain to uniquely identify your email traffic and provide access to your traffic analytics.

Tip: Authentication domain can be either the domain-name or the sub-domain. If it’s a domain-name, the data will show the traffic aggregated over any and all sub-domains of that domain-name, plus any traffic corresponding to the (exact) domain-name match. You can also independently add multiple sub-domains and view data about each of them separately.

  1. Go to
  2. On the bottom-right, click the + button.
  3. In the box that pops up, enter your authentication domain.
  4. Next, prove that you own the domain by adding a DNS TXT or a DNS CNAME record.


  • Each account needs a separate DNS verification record, and you won’t be able to see your traffic analytics until you complete this step (although you can skip the step and add this later).