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Mailhardener blog

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Office 365 leaks BCC domains

Microsoft hosted Exchange, part of the Office 365 suite, suffers from a data leak that can unintentionally disclose the domain name of a BCC address to all recipients. Mailhardener was able to reproduce this behaviour, in this article we perform a full analysis of the issue.


The SPF lookup limit explained

An SPF policy may not require more than 10 additional DNS lookups to fully evaluate, exceeding the limit may cause deliverability issues. In this article we explain why, and how to prevent this issue.

BIMI logo

The current state of BIMI

In this blog post we'll have a look on what the current state of BIMI is, and answer some common questions.

Microsoft logo

Microsoft has begun sending SMTP TLS reports

Good news on the adoption of SMTP TLS reporting: since the 25th of August 2020, we are seeing SMTP TLS reports being sent by Microsoft!.

Mailhardener security rating

Mailhardener is now self-learning

The December release of Mailhardener introduces a new domain overview page, which is made possible thanks to the introduction of our new self-learning algorithm.

The all new self-learning feature gives you much better insights into the status of your domain security, with features such as forwarding detection and asset discovery.


SPF merge guide

A domain can have only one SPF record. If you need to authorize a new email service to use your domain, you must add the service to your existing SPF record.

In this article we'll show you how to add new SPF rules to your domain by combining records.

envelope and letter

The SPF redirect explained

The SPF redirect modifier is a lesser known feature of SPF that may cause some confusion about its intended use.

In this article we'll dive into SPF redirect, when (not) to use it and how to avoid common pitfalls with it.

illustration of envelopes

Do not flatten your SPF record

Flattening SPF records supposedly optimizes SPF, but often causes more problems than it intends to improve.

In this article we discus why you should not flatten SPF and what methods you should use instead to improve email deliverability.


Introducing hosted MTA-STS

Mailhardener now has full support for MTA-STS and SMTP TLS reporting.

We are also proud to introduce hosted MTA-STS as part of the Mailhardener suite.

Google Cloud logo

How to enter TXT values in Google Cloud DNS

Google's popular Cloud DNS service is mostly excellent, but the interface is rather confusing when it comes to adding `TXT` type records.

In this blog post, we'll explore how to work with TXT records in Google Cloud DNS, and how to fix the 'invalid record data' error.


5 common mistakes with SPF

At Mailhardener, we analyse many domains for email security on a daily basis. This puts us in a unique position to list the most common made mistakes.

In this blog post, we'll discus the 5 most common made mistakes in SPF.