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What causes a 550 Invalid Domain error from Virgilio and Libero and how can it be resolved?

Summary

The "550 Invalid Domain" error, particularly when encountered with Italian mailbox providers (MBPs) like Virgilio and Libero, can be perplexing. While the error message itself points to an invalid domain, investigations often reveal more nuanced underlying causes than a simple DNS issue. This error signifies a permanent failure, meaning the recipient server has rejected the email due to a perceived problem with the sender's domain or authentication setup. Understanding the interplay between sender configuration, DMARC policies, and the recipient server's specific interpretations is crucial for resolution.

What email marketers say

Email marketers grappling with the "550 Invalid Domain" error from Virgilio and Libero often find themselves in a perplexing situation due to the ambiguous nature of the bounce message. Their experiences highlight a strong suspicion that DMARC alignment plays a significant, albeit indirectly communicated, role in these rejections, especially when sending through third-party platforms that may not fully support custom authentication configurations for the sender's domain.

Marketer view

Email marketer from Email Geeks suggests looking into sending domains when encountering a new bounce type like this, as it often points to issues with the sender's identity.

03 Jun 2020 - Email Geeks

Marketer view

Email marketer from Email Geeks suspects that the issue could be DMARC related, especially if the user's from address has a DMARC record, but the ESP doesn't allow custom DKIM, leading to alignment failures.

03 Jun 2020 - Email Geeks

What the experts say

Email deliverability experts offer a more granular perspective on the "550 Invalid Domain" error, dissecting the technical components of the bounce message and the intricate behaviors of Mailbox Providers. While some initial reactions might dismiss DMARC as a factor, the consensus leans towards its involvement, particularly given the known aggressive DMARC interpretation by certain Italian ISPs. Experts stress the importance of understanding the full SMTP transaction and proper sender authentication beyond basic setup.

Expert view

Expert from Email Geeks states that the message indicating an invalid FQDN like "smtp-41.iol.local" is accurate because '.local' is a reserved gTLD per RFC 6762 and cannot be resolved by internet DNS servers.

03 Jun 2020 - Email Geeks

Expert view

Expert from Email Geeks suggests that the message from the MBP referencing "smtp-41.iol.local" indicates this '.local' component either comes from the sender's HELO command or is an internal configuration issue leaking from within the MBP itself.

03 Jun 2020 - Email Geeks

What the documentation says

Official documentation and internet standards provide the foundational understanding of what constitutes a valid domain and how email transactions should behave. While they don't explicitly address the peculiar "550 Invalid Domain" error from Virgilio and Libero, they outline the rules and expectations that, when not met, can lead to such rejections. Understanding these standards is key to debugging complex deliverability issues.

Technical article

Documentation from RFC 6762 states that the '.local' Top-Level Domain is designated as a special-use domain name reserved exclusively for private use within local area networks and is not designed for public internet resolution.

21 Feb 2013 - RFC 6762

Technical article

SMTP Documentation outlines that a 550 permanent failure error signals that the requested action could not be completed because the recipient mailbox is unavailable, or there is a fundamental issue preventing message delivery from the sender to the recipient.

15 Jan 2019 - SMTP Documentation

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