Mail Server IP Blacklist Removal for @t-online.de

#1

First of all, many thanks for topic " Mail Server IP Blacklist Removal Tips to Improve Email Deliverability" which helped me solved the problem with email cannot reach @gmx.de and @web.de.

Since we have some customers from Germany and using t-online@de email domain. Our email server is based on CentOS 8, and I am using postfix as MTA.
The error message likes below:
Error Message: refused to
talk to me: 554 IP=1xx.xxx.xxx.xxx - A problem occurred. (Ask your
postmaster for help or to contact [email protected] to clarify.) (BL)

I have sent a request email to the email address above, but they replied like:

"
thank you for your message.
Please note that hosts which are de facto anonymous to third parties are
not qualified for delisting at our system. See the information in our
“Postmaster FAQ” at https://postmaster.t-online.de/index.en.html,
especially chapter 4.1:
"

I have read the documentation and still have no idea how to solve this issue.
BTW, our email server not on the blacklists like:
Spamhaus
mxtoolbox
dnsbl
cyren

Thanks in advance.

#2

You should have a PTR record, which is a record for IP address. You should set PTR record to your mail server hostname.

Then the hostname of your PTR record should resolve back to the same IP address. This indicates you own/manage the IP address.

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#3

Guide: How to bypass email blacklists

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