Email Authentication: SPF, DKIM, and DMARC Best Practices

Outlook Postmaster(y) page

IMPORTANT UPDATE 02/04/2025: Outlook announced on their Community Blog that they will enforce requirements for High Volume sender starting May 5, 2025. To help the sender community, we are glad to share our experiences collected over the years with some ISPs. This page concerns Outlook.com, whose webmail is one of the most widely used in […]

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Categories: Authentication, Deliverability, ISP

PowerMTA 5.0: Using a proxy for email delivery

One new thing we are particularly excited about is PowerMTA 5.0 support for forward proxies: this allows delivery from IPs which don’t need to be co-located on the same server or subnet. In this blog post, we will explain this with a few use cases and introduce Postmastery’s MTA proxy for a ready-to-go solution. Use […]

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Categories: Authentication, Deliverability, General, PowerMTA

Google Postmaster Tools (GPT) unlocked via Postmastery Delivery Analytics

Postmastery took an important step in their objective to monitor all relevant email delivery metrics in one application: adding Google Postmaster Tools data. What is Google Postmaster Tools (GPT) For senders that monitor their reputation, Google Postmaster Tools (GPT) is an important resource. For those who haven’t yet heard about it, GPT is a website […]

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Categories: Authentication, Deliverability, General

PowerMTA 5.0 released

On 17 September, PowerMTA 5.0r1 was released. This is the first general availability (GA) release. Before this release PowerMTA 5.0 was tested in a long beta programme. Various new PowerMTA features Probably the biggest change since 4.5 is the completely new web monitor. The web interface is now a modern ‘single page application’ (SPA). The […]

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Categories: Authentication, General, PowerMTA

Check your (Power)MTA settings: Numericable and Noos MXs records moved to SFR

In 2014, French ISPs Numericable and SFR merged to become the Altice France group. Numericable was itself the result of a merger between NC Numericable and Noos in 2007.   Up to now, mailboxes at these ISPs were managed independently using different MXs and anti-spam protection. Noos and Numericable domains on one end and SFR domains […]

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Categories: Authentication, Deliverability, General, Postfix, PowerMTA, Providers

Brand Indicators for Message Identification (BIMI) ready for take off?

BIMI is the new open standard for visualising your brand in the recipient’s mailbox with an image. Why BIMI? The new standard uses DMARC, leading some to call BIMI ‘DMARC 2.0’. While almost all previous authentication and identification methods work in the background, BIMI is the first to really try to visualise and strengthen your […]

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Categories: Authentication, DMARC, General

Proper MIME prevents DKIM failures in Outlook

At Postmastery, we work for various ESPs and brands to optimise email delivery. Recently, one of our clients faced a mysterious DKIM failure when sending mail to Outlook.com domains. (A generic explanation of what DKIM is and how it works is available on dkim.org.) Analysing SMTP headers First thing we did was to analyse the client’s […]

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Categories: Authentication, General

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