What are the deliverability implications of using Mailmend for email sending?
Michael Ko
Co-founder & CEO, Suped
Published 20 May 2025
Updated 18 Aug 2025
6 min read
Email deliverability is a complex dance between senders and mailbox providers. It is not just about whether an email is delivered, but whether it reaches the recipient's inbox rather than the spam or junk folder. This distinction is crucial for any successful email campaign. A high deliverability rate ensures your messages are seen, while a low rate can render even the best content ineffective.
Recently, a tool called Mailmend has gained attention, claiming to help emails bypass spam filters. This claim, however, immediately raises red flags within the email deliverability community. Tools that promise to circumvent standard email filtering mechanisms often employ tactics that are, at best, ethically questionable and, at worst, outright harmful to your long-term sender reputation.
I've explored discussions around Mailmend and similar services, and while some users might report temporary success, the underlying methods present significant risks. It is important to understand what these tools do and the potential deliverability implications before considering their use. The goal should always be sustainable inbox placement, not short-lived filter evasion.
Understanding Mailmend's approach
Mailmend, and services like it, reportedly use techniques such as injecting hidden content or hashbusters into emails. This involves adding seemingly random text or code elements that are invisible to the recipient but are intended to alter the email's fingerprint and confuse spam filters. The idea is to make each email appear unique, preventing filters from easily identifying and blocking repeat offenders or specific mail streams.
However, this approach directly contradicts fundamental guidelines set by major mailbox providers. Gmail, for example, explicitly warns against such practices. Their sender guidelines advise against using HTML and CSS to hide content in messages, stating that it can lead to emails being marked as spam. This isn't a minor suggestion, it's a clear directive from one of the largest email providers.
Gmail's stance on hidden content
Hiding content within emails, often through obscured HTML or CSS, is a deceptive practice that undermines trust and directly violates the principles of transparent email communication. Mailbox providers actively work to detect and penalize such methods.
Violates guidelines: Major providers like Google (Gmail) clearly state that hiding content can lead to emails being marked as spam.
Spam tactic: This technique is historically associated with spammers trying to bypass filters, not legitimate senders.
Erosion of trust: Using such methods suggests an intent to deceive, which erodes trust with both mailbox providers and recipients.
These techniques are essentially a form of spam trickery, attempting to fool sophisticated filtering systems. While they might offer a momentary advantage, the effectiveness is fleeting. Mailbox providers are constantly evolving their algorithms, often utilizing advanced AI, to detect and counteract such evasion tactics.
The risks to your sender reputation
The primary risk of using a tool like Mailmend lies in the damage it can inflict on your sender reputation. Mailbox providers track various signals to determine if your emails are legitimate, including engagement, spam complaints, and adherence to best practices. When they detect attempts to hide content or manipulate delivery, it severely degrades your reputation, regardless of your other sending habits.
This isn't a grey area; it is considered a black hat tactic. While it might trick filters for a short period, it's a game of cat and mouse where the senders (and their tools) will inevitably lose. Once caught, the consequences are severe and long-lasting, far outweighing any perceived short-term gains. It tells mailbox providers that you are not a legitimate sender.
Short-term perception
Initially, you might see a bypass of some spam filters, leading to a false sense of security. The hidden content can momentarily confuse less sophisticated systems, allowing emails that would otherwise be flagged to reach the inbox. This period is often brief and unsustainable.
Long-term reality
Mailbox providers are constantly adapting. Once these tactics are detected, your domain and IP address can be blocklisted. This results in widespread delivery failures, severely impacting your ability to reach subscribers and undoing all your hard work.
When your sender reputation drops, it affects all your email sending, not just the campaigns using Mailmend. It becomes harder to land emails in the inbox, even legitimate ones. This ripple effect can lead to decreased open rates, click-through rates, and ultimately, a significant hit to your return on investment.
Long-term deliverability consequences
The long-term deliverability consequences of using tools like Mailmend are severe. Once your domain or IP is identified for using these unethical methods, you risk being permanently blocklisted by major mailbox providers. Recovery from a bad reputation or a widespread blocklist (or blacklist) can be a lengthy and arduous process, sometimes taking months or even years.
Beyond just getting blocklisted, using such methods can also lead to a substantial loss of your subscriber base. If your emails consistently land in spam folders, recipients will stop seeing them, leading to decreased engagement and eventually, a cleanup of inactive or unengaged subscribers. This directly impacts the value of your email list and future marketing efforts.
For sustainable deliverability, focusing on legitimate practices is paramount. This includes proper email authentication using SPF, DKIM, and DMARC. These protocols prove that your emails are legitimate and authorized by your domain, building trust with mailbox providers and ensuring better inbox placement. Without proper authentication, even well-intentioned emails can fail.
Instead of seeking shortcuts, invest in understanding how email deliverability truly works and implementing practices that foster a strong, positive sender reputation. This includes maintaining a clean email list, sending relevant content, and monitoring your email performance consistently. Ultimately, genuine engagement is key to long-term success, not evasion tactics.
Prioritizing legitimate sending practices
The discussions I've seen among email professionals highlight a clear consensus: tools that promise to bypass spam filters using hidden content or similar methods are universally considered harmful. While they might provide a fleeting moment of inbox glory, they ultimately jeopardize your entire email program. Mailbox providers are increasingly sophisticated, and these outdated tactics are quickly detected.
Instead of trying to outsmart the system, the most reliable path to excellent deliverability is through adherence to industry best practices. This means building your sender reputation through consistent volume, positive recipient engagement, and strict list hygiene. A legitimate sender doesn't need to hide anything in their emails.
My recommendation remains clear: prioritize ethical and transparent email sending practices. Focus on delivering value to your subscribers, ensuring proper email authentication is in place, and continuously monitoring your email performance. This approach not only safeguards your deliverability but also builds a sustainable and trustworthy relationship with your audience and mailbox providers.
Views from the trenches
Best practices
Maintain a clean and engaged email list, regularly removing inactive subscribers to boost sender reputation.
Implement strong email authentication protocols like SPF, DKIM, and DMARC to verify sender identity and prevent spoofing.
Consistently monitor your deliverability rates and spam complaint feedback loops to identify and address issues promptly.
Focus on sending valuable, relevant content that recipients genuinely want to receive, encouraging positive engagement.
Common pitfalls
Relying on hidden content or obfuscation techniques to bypass spam filters, leading to severe penalties and blocklisting.
Ignoring email authentication settings, making your emails appear untrustworthy to mailbox providers.
Failing to segment your audience or personalize content, resulting in low engagement and increased spam complaints.
Sending emails to purchased or unverified lists, which often contain spam traps that destroy sender reputation.
Expert tips
Always prioritize building a strong sender reputation through ethical practices; shortcuts like hidden content lead to long-term harm.
Mailbox providers are increasingly sophisticated; old spammer tricks are quickly detected and penalized.
Recovery from blacklisting due to deceptive practices is a lengthy and challenging process, often resulting in significant list loss.
Focus on creating genuinely wanted emails; that's the only sustainable path to the inbox.
Expert view
Expert from Email Geeks says: Using hashbusters is an old spammer technique intended to bypass filters, and those who use it are actively declaring they don't care about permission.
July 29, 2024 - Email Geeks
Marketer view
Marketer from Email Geeks says: Such methods are clearly black hat, not merely grey, and it's difficult to believe these old SEO trickery tactics still work with today's advanced AI algorithms.
Google (Gmail) clearly state that hiding content can lead to emails being marked as spam.
