What is ESP Sidekick, how does it work, and is it safe to use on different operating systems?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 Jun 2025
Updated 19 Aug 2025
6 min read
When discussing email deliverability, the term 'ESP Sidekick' sometimes comes up, but it can be a bit confusing. Unlike common interpretations of 'Sidekick' as a browser or a Wi-Fi analysis tool like the Ekahau Sidekick, in our context, we are referring to a specific desktop application designed to interact with Google Postmaster Tools. This tool aims to automate the process of checking domain reputation, spam rates, and other crucial metrics that inform your email program's health.
The primary goal of such a tool is to streamline the daily or weekly task of monitoring various domain metrics reported by Google Postmaster Tools. For email senders managing many domains or needing frequent updates, manual checks can become tedious and time-consuming. An automated tool promises to retrieve this data more efficiently, providing insights without constant manual intervention.
Understanding how these tools operate, especially concerning their safety and compatibility across different operating systems, is crucial for anyone considering their use. Given that Google does not offer a public API for its Postmaster Tools, any third-party solution must employ alternative methods to access this data.
How ESP sidekick works
At its core, ESP Sidekick functions by automating web browsing to access and extract data from Google Postmaster Tools. This is commonly referred to as web scraping or browser automation. Unlike tools that integrate directly via an official API, ESP Sidekick essentially mimics a human user's actions: navigating to the Postmaster Tools website, logging in, and then programmatically extracting the displayed information, such as domain reputation, IP reputation, and spam rates.
This method often involves libraries like Selenium, which can control a web browser programmatically. The software would typically open a hidden (or visible) browser instance, navigate to the Postmaster Tools login page, input credentials, and then parse the HTML content of the relevant dashboards to collect the required data. The extracted data is then usually compiled into a report, such as a CSV file, for the user to review.
Data Extraction: It scrapes relevant metrics like spam rate and domain reputation directly from the web page.
Reporting: The collected data is compiled into a readable format, often a CSV file, for easy analysis.
While this method can be effective for data retrieval, it inherently carries certain implications, particularly regarding security, as it relies on reverse-engineering a web interface rather than using a stable, officially supported API. This means that any changes Google makes to their Postmaster Tools interface could potentially break the functionality of such a scraping tool, requiring frequent updates.
Security implications
The safety of using ESP Sidekick is a critical concern, primarily because it's a third-party executable. Running any unverified software carries inherent risks. When a tool relies on screen scraping rather than an official API, you entrust it with access to sensitive information, in this case, your Google account credentials and data within Postmaster Tools. The biggest question is, what does the software do with this information?
Potential risks of unverified software
Data Security: Without open-source code or a clear security audit, there's no way to verify how the tool handles your login credentials or if it dials home with your data.
Malware Risk: Running a .exe file from an unknown source can expose your system to viruses, spyware, or other malicious software.
Account Suspension: Google's terms of service generally prohibit automated access to their services without an official API. Using a scraping tool could lead to your Google account being flagged or even suspended.
For these reasons, many email professionals and security teams would advise against using such a tool unless its code is open-source and has been thoroughly vetted. Transparency allows for inspection of its behavior, ensuring it only performs the advertised functions and doesn't pose a security risk.
Before considering any such tool, it is paramount to consult your organization's security policies and ensure compliance. Prioritizing the security of your data and email infrastructure should always be the top concern over convenience, especially when dealing with critical sender reputation metrics.
Operating system compatibility and challenges
Regarding operating system compatibility, the original ESP Sidekick tool was reportedly built for Windows, distributed as an executable (.exe). This immediately limits its native usability on other operating systems like macOS or Linux. Running Windows-specific executables on non-Windows systems usually requires compatibility layers or virtual machines.
Windows
The tool is natively compiled for Windows operating systems, meaning it can be run directly. However, the security considerations discussed previously still apply.
macOS and Linux
To use it on macOS or Linux, you would typically need to set up a virtual machine running a Windows environment. Alternatively, some users might try compatibility layers like Wine on Linux, but success is not guaranteed and can introduce further complexities and potential vulnerabilities.
The need for a Windows environment on other operating systems adds another layer of complexity and potential security risk. It also means increased resource consumption, as you would be running an entire virtual operating system just for one application. For those managing many domains, a dedicated virtual private server (VPS) running Windows might be considered, though this again raises questions about data handling and privacy.
The lack of official cross-platform support and reliance on a .exe file further underscores the importance of caution and due diligence before integrating such a tool into your workflow, especially in a professional setting where data privacy and security are paramount.
Considering alternatives
While tools like ESP Sidekick offer an enticing shortcut for monitoring Google Postmaster Tools data, the security concerns associated with running unverified software and the lack of native cross-platform support present significant challenges. Given the sensitivity of email deliverability data and the potential impact on your sender reputation, a cautious approach is highly advisable.
Relying on solutions that require scraping or bypassing official API channels can lead to instability if the target website's structure changes. A more robust and secure approach involves utilizing established email deliverability platforms that integrate with official APIs (where available) or provide their own verified methods for collecting and presenting critical email performance metrics, including blocklist (or blacklist) monitoring and DMARC reports.
Views from the trenches
Best practices
Always prioritize official APIs or well-documented integration methods when available for data access.
Regularly monitor your domain and IP reputation using legitimate Postmaster Tools dashboards and other trusted sources.
Implement strong email authentication protocols like DMARC, SPF, and DKIM to build and maintain trust with mailboxes.
Maintain a clean mailing list and send relevant content to avoid spam complaints and maintain positive sender reputation.
Educate your team on the risks associated with running unverified third-party software for critical tasks.
Common pitfalls
Relying on screen-scraping tools that can break unexpectedly due to website interface changes.
Ignoring security warnings related to running unverified executables downloaded from the internet.
Failing to consider potential terms of service violations with service providers by using unauthorized access methods.
Neglecting to manually verify the data output by automated tools, especially if their methodology is opaque.
Assuming a tool is safe simply because it is shared within a community without independent vetting.
Expert tips
Validate any third-party tools with your security team or an IT professional before deployment.
Use virtual machines or isolated environments if testing unverified software to minimize risk to your primary system.
Focus on foundational deliverability practices to improve reputation, rather than relying solely on reporting shortcuts.
Consider contributing to open-source projects for similar tools if you need custom solutions, ensuring transparency.
Keep abreast of updates and changes to Postmaster Tools and other monitoring services for future planning.
Marketer view
Marketer from Email Geeks says they don't think their security team would approve of using a tool like this, and they are concerned about what happens to their data and if it sends information back home.
2019-07-01 - Email Geeks
Expert view
Expert from Email Geeks says they are curious how the tool is built given that Google Postmaster Tools does not have an official API.
2019-07-02 - Email Geeks
Summary and best practices
While ESP Sidekick offered a unique approach to accessing Google Postmaster Tools data, its reliance on web scraping and status as an unverified executable present notable security and compatibility considerations. The absence of an official API for Google Postmaster Tools means any third-party tool must navigate these complexities.
For serious email marketers and senders, prioritizing robust, transparent, and secure solutions for email deliverability monitoring remains paramount. This often involves combining official tools with reputable deliverability platforms that offer comprehensive insights without compromising security or system integrity.
Windows, distributed as an executable (.exe). This immediately limits its native usability on other operating systems like 
macOS or 
Linux. Running Windows-specific executables on non-Windows systems usually requires compatibility layers or virtual machines.
