How do BCC emails impact sender reputation and deliverability, especially during IP warming?
Matthew Whittaker
Co-founder & CTO, Suped
Published 25 Jun 2025
Updated 15 Aug 2025
9 min read
BCC (Blind Carbon Copy) emails are often used for various business reasons, such as internal archiving, compliance, or simply keeping a record of sent communications. While seemingly harmless, the way these emails interact with mailbox providers can significantly impact your sender reputation and overall deliverability, especially during the critical phase of IP warming.
Sender reputation is the cornerstone of email deliverability. Internet Service Providers (ISPs) and mailbox providers (like Gmail and Microsoft) continuously monitor your sending behavior to determine if your emails are legitimate or potentially spam. A positive reputation signals that you are a trustworthy sender, leading to better inbox placement.
IP warming is the process of gradually increasing the volume of emails sent from a new IP address. This slow ramp-up helps establish a positive reputation with mailbox providers, showing them that you are a legitimate sender. During this delicate period, every interaction metric, such as open rates, click-through rates, and complaint rates, is under intense scrutiny.
The core issue with BCC emails, especially during IP warming, is their potential to skew these vital metrics. If these BCC copies are sent to mailboxes that are unlikely to engage with the content, they can inadvertently harm your overall sender reputation and undermine your deliverability efforts. This guide will explore how BCC emails impact your email performance and provide strategies to navigate these challenges effectively.
The unseen impact of BCC on deliverability
When an email is sent with BCC recipients, the receiving mailbox provider does not inherently know that those recipients are on the blind carbon copy list. From their perspective, each recipient address, whether in the 'To', 'CC', or 'BCC' field, is treated as a direct recipient of the email. This fundamental aspect is crucial for understanding how BCC impacts deliverability.
The main problem arises because BCC copies, especially those sent to internal archives or monitoring mailboxes, typically experience extremely low engagement. They are rarely opened, clicked, replied to, or moved out of the spam folder. Mailbox providers interpret this lack of engagement as a negative signal about your sending practices. A high volume of emails with low engagement can suggest that your content is not relevant, or worse, that it is unsolicited spam.
Over time, consistently low engagement metrics from a significant portion of your sent volume can degrade your sender reputation. Mailbox providers use these signals to decide whether to place your emails in the inbox, spam folder, or even block them entirely. A tarnished reputation can lead to legitimate emails being filtered into spam or even being rejected outright, making it difficult to reach your intended audience. This can eventually lead to your domain or IP address ending up on a blacklist.
If you are BCCing copies to email addresses hosted by major providers like Gmail or Microsoft, their systems will record the lack of interaction. This directly affects your sending reputation with those providers, even if the primary recipients are engaging positively. The aggregate data from all recipients, including BCC, contributes to your overall sender score.
BCC and IP warming challenges
IP warming is a critical process for new senders or those transitioning to a new IP address. It involves a phased approach to sending emails, gradually increasing volume over days or weeks. This allows mailbox providers to observe your sending habits and build trust in your IP. The goal is to demonstrate consistent, positive engagement from a growing audience. More details on this process can be found in resources like Iterable's guide to IP warm-up.
Introducing a high volume of unengaged BCC emails during IP warming can severely undermine this delicate process. If your warming schedule dictates a certain volume for a given day, and a significant portion of that volume consists of BCC copies that receive no interaction, it creates a false impression of poor engagement for your primary sends. Mailbox providers might see a high send volume but a disproportionately low open or click rate, leading them to quickly flag your IP as suspicious.
This can lead to a stalled or even reversed warming process. Instead of building a positive reputation, you could be quickly damaging it, resulting in emails landing in spam folders or being outright blocked. It essentially signals to ISPs that your emails are not valuable to recipients, a direct contradiction to the purpose of IP warming.
When planning your IP warming strategy, it is essential to consider all email volume, including any BCC copies. These emails must be factored into your daily or weekly sending limits. If you're sending to Gmail customers, for example, the volume of your internal BCC copies going to Gmail mailboxes will contribute to your overall send volume and can impact your Google Postmaster Tools reputation and deliverability metrics.
Mitigating risks and alternatives
While BCC is generally not advisable for bulk email, especially during IP warming, I understand that sometimes there's a legitimate business need to keep copies of sent emails. In such cases, it's crucial to explore alternatives that don't compromise your sender reputation. The key is to avoid sending unengaged emails through your primary sending infrastructure.
One effective alternative is to use internal logging or journaling systems within your email infrastructure or CRM. Instead of BCCing a copy to an actual email address, configure your sending platform to automatically log or archive all outgoing emails. This achieves the record-keeping purpose without sending additional emails that could negatively impact your engagement metrics. If you must send internal copies, consider routing them through a separate, dedicated IP address not used for primary customer communications, or use a mailbox you own and can whitelist.
Another consideration is to implement internal rules for BCC'd emails if they are sent to a mailbox you control. For example, you could set up a rule that automatically marks these emails as read and moves them to a specific folder. While this doesn't generate positive engagement signals like clicks, it prevents them from sitting as unopened inboxes, which could be interpreted more negatively by mailbox providers monitoring engagement data.
Ultimately, the best approach is to minimize the use of BCC for high-volume email campaigns, especially during IP warming. If it's unavoidable, carefully assess the volume of BCC copies and how they might impact your overall engagement metrics. Prioritize direct recipient engagement and explore technical solutions that satisfy internal record-keeping needs without adding unnecessary deliverability risk.
Maintaining sender health
BCC emails, while convenient for internal record-keeping, pose significant challenges to sender reputation and deliverability, particularly during the crucial IP warming phase. The fundamental issue is that mailbox providers do not differentiate between 'To' and 'BCC' recipients in terms of their impact on your sending metrics. All unengaged recipients, regardless of how they received the email, contribute to a negative reputation.
During IP warming, this effect is amplified. The goal of warming is to build trust through consistent, positive engagement from a growing volume of emails. If a large portion of this volume consists of BCC copies that remain unopened or unclicked, it sends conflicting signals to ISPs, potentially halting or even reversing your warming progress. This can lead to increased spam folder placement and blocklisting.
To maintain a healthy sender reputation, focus on ensuring that every email sent contributes positively to your engagement metrics. This means actively managing your recipient lists, prioritizing engaged subscribers, and avoiding practices that introduce unengaged volume into your sending streams. Alternatives like internal logging or CRM integrations are far safer for record-keeping than traditional BCC.
Remember, the success of your email deliverability hinges on how mailbox providers perceive your sending behavior. By understanding the nuances of how BCC impacts this perception and adopting best practices, you can protect your sender reputation and ensure your emails consistently reach the inbox.
Views from the trenches
Best practices
Monitor engagement metrics from your primary recipients closely to avoid skewing IP warming data.
For internal archiving, use journaling or logging systems instead of blind carbon copy.
If internal BCC is essential, implement rules to mark those emails as read and filed to mimic engagement.
Ensure that the volume of unengaged BCC emails does not disproportionately inflate your total send volume.
Consider alternative methods like CRM integrations for internal record-keeping to avoid deliverability risks.
Common pitfalls
Sending high volumes of BCC emails during IP warming without tracking their engagement.
Assuming mailbox providers don't treat BCC recipients the same as 'To' recipients for reputation.
Not accounting for the low engagement of internal BCC copies when calculating overall send volume.
Experiencing unexpected dips in sender reputation and increased spam folder placement.
Relying on BCC for critical internal record-keeping, which introduces unnecessary deliverability risks.
Expert tips
Expert from Email Geeks says that when a BCC'd email is received, mailbox providers do not discern it as a blind copy, treating all recipients equally.
Expert from Email Geeks says that sending BCC copies via an ESP back to the sender's mailbox provider can create significant deliverability challenges.
Expert from Email Geeks says that internal BCC should not affect ISP delivery unless the internal mail is hosted by the same ISP.
Expert from Email Geeks says that some engagement data might carry over between Microsoft 365 and G Suite and their consumer counterparts, though the extent is not always certain.
Expert from Email Geeks says that a high volume of unengaged internal BCC emails can lead to reputation dips and spam folder placement, even with a previously pristine reputation.
Expert view
Expert from Email Geeks says that when a BCC'd email is received by a mailbox provider, it is not evident that it's a BCC, and the recipient email address is treated as a direct 'To' recipient.
April 13, 2020 - Email Geeks
Expert view
Expert from Email Geeks says that sending BCC emails via an Email Service Provider back to the sender's mailbox provider can be problematic and broadly, BCC is not advisable for bulk emails, especially during IP warming.
Gmail and 
Microsoft) continuously monitor your sending behavior to determine if your emails are legitimate or potentially spam. A positive reputation signals that you are a trustworthy sender, leading to better inbox placement.
