How to improve email deliverability for solicited business proposals to corporations?
Michael Ko
Co-founder & CEO, Suped
Published 5 Jul 2025
Updated 17 Aug 2025
8 min read
The challenge of ensuring email deliverability for solicited business proposals to large corporations is unique. Even when a prospect explicitly requests a proposal after a conversation, your email can still end up in their spam folder. This isn't just frustrating, it directly impacts your ability to close deals and grow your business. Corporate spam filters are incredibly aggressive, designed to protect vast networks from malicious content and unsolicited pitches.
What often looks like a legitimate, expected communication to you might trigger numerous red flags for these sophisticated systems. Factors like email content, attachments, sending infrastructure, and even the history of your sending domain all play a role. It requires a nuanced approach that combines robust technical setup with thoughtful communication strategies to consistently land your proposals in the inbox.
Understanding corporate spam filters
Even though your business proposals are solicited, corporate spam filters often treat them with extreme scrutiny. These filters are not always intelligent enough to discern context, such as a prior face-to-face meeting or verbal invitation. Instead, they rely on a complex algorithm of signals, many of which can inadvertently be triggered by proposal emails. The goal of these filters is to err on the side of caution, blocking anything that even remotely resembles a threat or an unwanted intrusion.
Corporate filters are particularly wary of attachments. PDFs, Word documents, and other common proposal formats are frequently exploited by malicious actors for malware delivery. Even if your files are clean, the mere presence of an attachment, especially in a first-time communication to a large organization, can elevate its spam score. Furthermore, certain keywords or phrases commonly found in business proposals can mimic spammy marketing language, leading to a higher likelihood of being flagged.
Beyond content, tracking domains used by CRM systems can sometimes be a red flag. While valuable for analytics, these trackers add an extra layer of complexity to your email's journey through a corporate network. If a tracking domain has a poor reputation or is frequently associated with unwanted emails, it can negatively affect your deliverability, regardless of the quality of your message or the recipient's expectation.
The risk of attachments
Attaching PDFs or Word documents can significantly increase the chances of your solicited business proposal landing in spam. Corporate email systems are designed to block known malware vectors, and these file types are often used for such purposes.
Optimizing your initial outreach and content
The first email you send after a meeting is crucial. Instead of immediately sending a lengthy proposal with attachments, consider a simpler, engagement-focused initial message. This "ice-breaker" email aims to establish a positive interaction and signal to the recipient's mail server that your subsequent communications are desired. A short, concise email that references your recent conversation and asks a simple question can encourage a reply, which is a strong positive signal for deliverability.
Once you receive a reply, the communication channel is effectively "opened." This positive engagement history can significantly improve the chances of your full proposal landing in the inbox. It demonstrates to spam filters (and human recipients) that you have an established, welcomed dialogue. Think of it as warming up the recipient's inbox for your actual proposal.
Your email content itself requires careful consideration. While your proposals are professional, ensure the language isn't overly promotional or uses phrases commonly associated with mass marketing emails. Avoid excessive bolding, all caps, or an abundance of links. Keep your email signature concise and professional, minimizing image and link density, as these can also contribute to a higher spam score.
Current approach
Heavy content: Sending long emails with extensive details in the first outreach.
Attachments: Including large PDF or Google Docs files directly in the initial email.
CRM tracking: Utilizing tracking links that might flag spam filters.
Aggressive language: Using salesy or marketing-heavy phrasing that triggers filters.
Recommended approach
Ice-breaker email: Send a short, personalized follow-up without attachments.
Engagement first: Ask a simple question to encourage a reply and establish two-way communication.
Host files: Provide a link to your proposal hosted on a reputable service.
Clean content: Maintain professional, concise language and a minimalistic signature.
Technical foundations and reputation management
While your SPF, DKIM, and DMARC are correctly configured, it's vital to remember that technical setup is just one piece of the deliverability puzzle. Even with perfect authentication, your domain's reputation plays a critical role, especially when sending to large organizations. Corporate email systems rigorously assess sender reputation, and a domain with low volume or limited positive engagement can struggle, even if its authentication is solid. You can learn more about how to improve your email reputation and deliverability.
This DMARC policy tells receiving servers to reject emails that fail DMARC authentication and provides addresses for sending forensic and aggregate reports.
A common issue arises when sending through shared IP addresses or platforms, even if they integrate with trusted services like Google Workspace. If other senders on the same shared infrastructure are engaging in questionable practices, your email deliverability can be negatively impacted. Enterprise filters may block (or blacklist) IP ranges or even entire sending domains if they are associated with spam or suspicious activity. Regularly checking if your IP or domain is on a blocklist (or blacklist) can help proactively identify and address these issues.
For organizations heavily relying on Microsoft email services, particular attention is needed. Microsoft's spam filtering is known for being aggressive, and their systems can be quick to flag emails that don't align with their stringent criteria. Understanding their specific requirements and how to improve email deliverability to Microsoft and avoid spam filters is crucial. For instance, sometimes a sender's existing domain reputation can trigger filters on the recipient's side, even when replying to an inquiry.
Factor
Impact on solicited proposals
Best practice
Email authentication
Ensures legitimacy but doesn't guarantee inbox placement alone.
Low volume or negative signals can lead to spam folder placement.
Build positive engagement over time and monitor your domain health.
Shared sending IPs
Can suffer if other users on the same IP send spam.
Prefer dedicated IPs if volume permits, or choose a reputable sending service.
Attachments
High risk of triggering malware and content filters, even for legitimate files.
Host files externally and link to them instead of attaching.
Recipient's email provider
Providers like Microsoft have very strict filtering rules.
Tailor content and sending strategy for dominant recipient platforms.
Alternative approaches and continuous monitoring
For high-value, low-volume communications like business proposals, sometimes traditional email sending methods can fall short due to the aggressive nature of corporate spam filters. Consider using a reputable proposal sending service that specializes in secure document delivery. These services often host your proposal on their platform and send a simple, trackable link via email. This approach can bypass the attachment problem and leverage a service's established sending reputation, which might be more robust than an individual sender's domain for high-stakes B2B outreach.
While it might seem counterintuitive, some senders in niche, low-volume B2B scenarios have found success sending initial outreach from generic domains like Gmail (gmail.com) or Outlook (outlook.com), rather than their custom business domain. The theory is that these large providers have such massive, diverse sending volumes that their overall reputation can sometimes be more neutral, especially for low-volume senders who haven't built significant positive reputation on their custom domain. However, this is not a recommended long-term strategy for professional business communications, nor for marketing or newsletter sending, as shared domain reputation can be a "reputation crutch" that eventually fails. It's also important to ensure compliance with regulations like the CAN-SPAM Act, which sets rules for commercial email.
Consider specialized proposal services
Using a dedicated business proposal service can enhance deliverability by hosting documents securely and providing a clean link for email delivery. This helps avoid attachment-related spam flags and can leverage a strong sender reputation.
Ultimately, improving deliverability is an ongoing process that requires continuous monitoring and adaptation. Even after implementing best practices, corporate email environments are dynamic, with filters constantly evolving. Regularly testing your email deliverability (e.g., via seed list tests that target B2B filters) and paying attention to recipient feedback are crucial steps. This proactive approach allows you to identify and resolve issues quickly, ensuring your important proposals consistently reach their intended audience.
Views from the trenches
Best practices
Send a short, engagement-focused email first to get a reply before sending a full proposal.
Ensure files are delivered as links to hosted sites, not as direct attachments to emails.
Proactively monitor your domain's reputation and check for any blocklist (or blacklist) listings.
Build a consistent positive sending history with regular, welcomed communications.
Use a reputable proposal service to send proposals instead of attaching files.
Common pitfalls
Attaching PDFs or Word documents directly in the first email to corporate recipients.
Using overly promotional or "spammy" language in initial outreach.
Relying heavily on tracking domains that might be flagged by aggressive corporate filters.
Assuming solicited emails will bypass spam filters without any special considerations.
Not adapting sending strategies for specific recipient domains, especially Microsoft.
Expert tips
For very low volume, high-stakes B2B emails, a personal Gmail or Outlook.com address might occasionally land better than a custom domain with no established volume, but this is not for marketing emails or long-term strategy.
Engage recipients with a simple question in the initial email to prompt a reply, thereby improving future email deliverability.
Some enterprise filters are incredibly aggressive, and bypassing them often requires establishing a two-way conversation first.
Dedicated sending domains generally build better long-term reputations than shared or rewritten domains.
If a significant number of recipients use Microsoft, be aware that their spam filtering can be particularly challenging.
Expert view
Expert from Email Geeks says: For initial outreach, avoid sending emails with attachments or direct pitches, instead send a brief "nice to meet you" message asking for confirmation of details to prompt a reply.
Jan 22, 2024 - Email Geeks
Marketer view
Marketer from Email Geeks says: It is a reality of sending to businesses that spam filters will often put wanted mail into the spam folder, so you need to proactively work around that.
Jan 22, 2024 - Email Geeks
Conclusion: Ensuring your proposals land in the inbox
Improving email deliverability for solicited business proposals to corporations is a multi-faceted challenge that extends beyond basic email authentication. It requires a strategic understanding of how corporate spam filters operate, a willingness to adapt your initial communication strategy, and continuous attention to technical details and sender reputation.
By prioritizing engagement, minimizing initial email complexity, leveraging secure document hosting, and maintaining a pristine sender reputation, you can significantly increase the likelihood that your solicited proposals reach the inbox, not the spam folder. Consistent effort in these areas will build trust with both recipients and their email systems, ensuring your crucial communications are delivered effectively.
Google Workspace. If other senders on the same shared infrastructure are engaging in questionable practices, your email deliverability can be negatively impacted. Enterprise filters may block (or blacklist) IP ranges or even entire sending domains if they are associated with spam or suspicious activity. Regularly checking if your IP or domain is on a blocklist (or blacklist) can help proactively identify and address these issues.
Microsoft's spam filtering is known for being aggressive, and their systems can be quick to flag emails that don't align with their stringent criteria. Understanding their specific requirements and how to improve email deliverability to Microsoft and avoid spam filters is crucial. For instance, sometimes a sender's existing domain reputation can trigger filters on the recipient's side, even when replying to an inquiry.
