Summary
When a single sales representative experiences email blocking issues while their colleagues do not, the causes are multifaceted, spanning technical configurations, content quality, recipient-side factors, and sending practices. Ultimately, the recipient decides what constitutes spam. Factors such as a flagged IP address, poor sender reputation stemming from spam complaints, and suboptimal list hygiene contribute significantly. Different sending infrastructures and inconsistent sending behavior, such as aggressive cold emailing, can trigger filters. Recipient-side filtering, content quality (including spammy phrases and lack of personalization), and technical configurations like missing SPF, DKIM, or DMARC records also play key roles. Adequate email address warm-up procedures are critical as well. SMTP error codes and the possibility of irritated mail administrators further add to the complexity.
Key findings
- Recipient-Centric Spam Determination: The determination of whether an email is considered spam ultimately rests with the recipient's email client.
- Sender Reputation and IP Address Flagging: A poor sender reputation and a flagged IP address greatly increase the chances of emails being blocked.
- Recipient-Side Filtering: Recipient email servers may implement specific rules or filters that disproportionately affect a particular sales representative.
- Suboptimal Content: Content containing 'spammy' phrases, lacking personalization, or failing to engage recipients can trigger spam filters.
- Poor List Hygiene: Sending emails to unengaged users or neglecting to verify email addresses can negatively impact deliverability.
- Inadequate Email Warm-Up: Insufficiently warming up new email addresses before bulk sending can lead to increased blocking rates.
- Varying Sending Infrastructure: Differences in email clients, ISPs, or SMTP servers among sales representatives can result in inconsistent deliverability.
- Inconsistent Sending Behavior: Sudden sending volume spikes, aggressive cold emailing, or sending to unsubscribed recipients can trigger filters.
- Missing Authentication Records: Lack of proper SPF, DKIM, and DMARC records can negatively affect deliverability.
Key considerations
- Prioritize Recipient Relevance: Always ensure that emails are wanted and relevant to the recipients to minimize spam complaints.
- Monitor Sender Reputation: Actively monitor sender reputation metrics and address any issues promptly.
- Implement Robust List Hygiene Practices: Regularly clean and verify email lists to remove unengaged users and invalid addresses.
- Standardize Sending Infrastructure: Adopt a standardized sending infrastructure across the sales team to ensure consistent deliverability.
- Regulate Sending Patterns: Avoid sudden sending volume spikes or aggressive cold emailing practices.
- Optimize Email Content: Create engaging, personalized content that avoids spammy phrases and is relevant to the recipients' interests.
- Implement Authentication Protocols: Properly configure SPF, DKIM, and DMARC records to authenticate emails and improve deliverability.
- Conduct Email Warm-Up: Properly warm up new email accounts over time before high-volume sending.
- Investigate Recipient-Side Issues: Explore any potential filtering rules or blocks implemented by recipient email servers.
What email marketers say
12 marketer opinions
When one sales representative's emails are blocked while others are not, the issue stems from various factors, ranging from sender-specific issues to recipient-side configurations. Sender reputation, IP address flagging, content quality, and email list hygiene play significant roles. Recipient-side filtering, potentially due to irritated administrators or specific security rules, can also lead to blocks. Inadequate email address warm-up, technical errors, or variations in sending behavior can further contribute to deliverability problems. Ultimately, a combination of sender-specific practices and recipient-defined policies determines whether an email is accepted.
Key opinions
- Sender Reputation: A poor sender reputation, due to previous spam complaints or blacklistings, significantly increases the likelihood of emails being blocked.
- Recipient-Side Filtering: Recipient email servers may have specific rules or filters blocking emails from a particular sales rep, irrespective of other reps' deliverability.
- Content Quality: Low-quality content, 'spammy' keywords, or lack of personalization can trigger spam filters and lead to email blocks.
- List Hygiene: Poor email list hygiene, including sending to unengaged users, is a primary driver of deliverability problems.
- Warm-up process: Not correctly warming up a new email address will result in a spike in blocked emails.
Key considerations
- Monitor Sender Reputation: Regularly monitor sender reputation using tools and services designed for this purpose.
- Review Email Content: Audit email content for 'spammy' keywords and ensure personalization to improve engagement and avoid triggering filters.
- Clean Email Lists: Implement rigorous list hygiene practices, including removing unengaged users and regularly verifying email addresses.
- Check Recipient-Side Configurations: Investigate whether recipient email servers have specific rules or filters affecting the blocked sales rep, by contacting the recipient.
- Warm up correctly: Warm up new emails over a period of time to avoid being flagged for spam.
Marketer view
Email marketer from NeilPatel.com shares that if one sales rep's IP address has been flagged for spam, even if the others haven't, their emails are more likely to be blocked.
29 Sep 2021 - NeilPatel.com
Marketer view
Email marketer from Reddit explains that sender reputation is key. If the one rep's email address or domain has a poor reputation due to previous spam complaints or blacklistings, their emails will be more likely to be blocked.
19 Sep 2023 - Reddit
What the experts say
3 expert opinions
The reason one sales rep's email is blocked while others aren't can be attributed to multiple factors. Ultimately, the recipient determines what is considered spam, regardless of the sender's intent. Technical differences in sending infrastructure (ISPs, email clients, SMTP servers) can lead to disparate treatment by receiving servers. Furthermore, inconsistent sending behavior, such as sudden volume spikes, aggressive cold emailing, or sending to unsubscribed recipients, can trigger filters and result in blocked messages for that specific rep.
Key opinions
- Recipient Determines 'Spam': The recipient's email client, not the sender, ultimately decides if an email is spam.
- Inconsistent Infrastructure: Variations in sending infrastructure among sales reps can lead to different treatment by receiving servers.
- Erratic Sending Behavior: Inconsistent sending patterns, particularly aggressive cold emailing or sending to unsubscribed recipients, can trigger filters.
Key considerations
- Recipient Perspective: Always consider the recipient's perspective and ensure emails are wanted and relevant.
- Standardize Infrastructure: Standardize the sending infrastructure across the sales team to ensure consistent deliverability.
- Monitor Sending Patterns: Monitor and regulate sending behavior to avoid sudden spikes or aggressive practices.
Expert view
Expert from Email Geeks explains that the sender can’t dictate if something is “spammy” or not - only the recipient can make that call. That’s the email client doing its job correctly.
16 Jun 2025 - Email Geeks
Expert view
Expert from Spam Resource explains that one potential reason is different sending infrastructures. If the sales reps are using different email clients, ISPs, or SMTP servers, their emails could be treated differently by receiving servers. This is especially true if one rep's setup has a poorer reputation or isn't properly configured.
28 Jun 2022 - Spam Resource
What the documentation says
4 technical articles
When a sales representative's emails are blocked while others aren't, various technical configurations and policies come into play. Google highlights the importance of adhering to Gmail's bulk sender guidelines, particularly setting up SPF, DKIM, and DMARC authentication. Microsoft's Exchange Online Protection (EOP) uses content filters, connection filtering, and Spam Confidence Levels (SCL) to block spam. RFC Editor details SMTP 550 errors, indicating refusal by the recipient server for reasons like sender blocks, spam flagging, or full mailboxes. Mimecast specifies that emails can be blocked because of content or if the email address has been previously blocked due to security policies.
Key findings
- Gmail Bulk Sender Guidelines: Failure to adhere to Gmail's bulk sender guidelines, especially regarding SPF, DKIM, and DMARC, can lead to blocks.
- Exchange Online Protection (EOP): Microsoft's EOP uses content filters, connection filtering, and SCL to identify and block spam.
- SMTP 550 Errors: SMTP 550 errors indicate the recipient server has refused the message due to various reasons.
- Content/Blocked Email Address: Mimecast blocks emails because of its contents or if the email has been previously blocked.
Key considerations
- Implement Authentication: Ensure SPF, DKIM, and DMARC authentication are correctly configured for the sending domain.
- Monitor Content: Review email content to avoid triggering spam filters or violating content policies.
- Check Block Lists: Verify that the sending email address or domain is not on any blocklists.
- Address SMTP Errors: Investigate and address the root cause of any SMTP 550 errors.
Technical article
Documentation from Mimecast details that an email may be blocked due to content within the email being blocked because of security policies setup. Also, the email address may have been blocked previously.
22 Aug 2022 - Mimecast
Technical article
Documentation from Microsoft explains that Exchange Online Protection (EOP) uses a variety of techniques to identify and block spam. It may be blocking emails from the one sales rep due to content filters, connection filtering, or spam confidence levels (SCL).
28 Feb 2025 - Microsoft Learn
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