Why are recipients exceeding their hourly email limit when BCC is used?
Summary
What email marketers say9Marketer opinions
Email marketer from SparkPost Support explains that if BCC recipients are largely unengaged or invalid addresses, it can significantly degrade sender reputation. ISPs may interpret this as a sign of spam, leading to aggressive rate limiting or blocking.
Email marketer from Reddit explains that using BCC extensively can trigger spam filters and throttling mechanisms because it masks the true recipients and can look like a spamming technique, especially if the list is not properly managed.
Email marketer from Email Marketing Forum user explains that using BCC in conjunction with certain email forwarding setups can cause SPF and DKIM authentication failures, leading to deliverability problems and potential rate limiting by receiving servers.
Email marketer from EmailOnAcid Blog shares how many ESPs treat BCC'd recipients the same as regular recipients when calculating sending reputation. High volumes of BCC'd emails, especially to unengaged addresses, can negatively impact sender reputation and lead to rate limiting.
Email marketer from Postmark App explains that using BCC for email marketing is bad practice. High sending volumes and potentially low engagement (as you don't track individual interaction) can hurt your reputation and increase throttling, which may result in hitting limit thresholds.
Email marketer from Quora explains that recipient email servers interpret BCC emails as individual emails sent to each recipient. If you BCC a large list, it can look like you're sending the same email repeatedly in a short time, which can trigger anti-spam measures and rate limits.
Email marketer from StackOverflow suggests that, while BCC itself doesn't directly cause over-limit errors, sending a massive number of emails in a short period (which BCC facilitates) can overload the mail server and trigger rate limiting.
Email marketer from Reddit explains how some ESPs might have internal limits on the number of BCC recipients allowed per email. Exceeding this limit can result in errors and sending failures, which may be misinterpreted as a general rate limit issue.
Email marketer from Mailgun Help Center explains that using BCC can cause the sending IP address to hit rate limits faster, as all BCC'd recipients count towards the hourly sending limit from that IP. This is because all emails appear to originate from a single source.
What the experts say4Expert opinions
Expert from Spam Resource explains that using BCC hides recipients from each other which prevents the server from getting a full view of the email recipient which increases the likely hood of the email getting marked as spam. It also reduces list hygiene.
Expert from Word to the Wise explains that extensive use of BCC can lead to deliverability problems and potential blocks as it is often associated with spam practices and may not allow for proper list management and engagement tracking.
Expert from Email Geeks confirms that BCC can cause bounces and incorrect domain attribution in bounce messages.
Expert from Email Geeks explains the root cause was a requirement to BCC someone within the organization on every email. The ESP wasn't showing these BCCs in the logs and was attributing the bounces to the recipients on the To: line.
What the documentation says4Technical articles
Documentation from AWS outlines the sending limits of SES. While not explicitly about BCC, it notes that all recipients (To, CC, and BCC) count towards your sending quota. Using BCC heavily can lead to quickly reaching these limits.
Documentation from Microsoft Docs explains that Exchange Online Protection (EOP) employs various limits to prevent spam and mass mailing abuse. These limits could be triggered if a large number of BCC recipients are included in a single email, causing the system to flag it as potential spam.
Documentation from Google Workspace Admin Help explains that Google Workspace has daily sending limits and rate limits designed to prevent abuse. Using BCC to send to a large number of recipients can quickly exhaust these limits, resulting in temporary sending restrictions.
Documentation from RFC Editor outlines SMTP standards and limitations. While RFC 5322 doesn't specifically address BCC, it implicitly defines limits on message size and recipient numbers that could impact large BCC sends. Exceeding these limits can cause delivery issues and potential rate limiting.