Summary
The question of whether fluctuating hourly email send volume within a large campaign impacts deliverability elicits divided opinions. Many prominent email service providers and deliverability firms strongly advise maintaining consistent, predictable sending patterns, stating that sudden hourly spikes or drops can negatively affect sender reputation and trigger spam filters. They emphasize that ISPs prefer stable sending behavior as an indicator of trustworthiness. However, a significant number of seasoned deliverability experts, particularly those active in community forums like Email Geeks, dismiss these granular hourly concerns for large, genuinely opted-in campaigns. They argue that such advice is often outdated, stems from misinterpretations of old warm-up strategies, or applies only to specific, less-than-ideal sending scenarios. For these experts, overall daily send volume consistency, strong sender reputation, and high recipient engagement are far more influential factors than precise hourly adjustments.
Key findings
- ISP Preference for Consistency: Many leading Email Service Providers, postmaster tools, and deliverability experts emphasize that Internet Service Providers (ISPs) prefer consistent, predictable sending patterns. Erratic or sudden hourly fluctuations can be flagged as abnormal, potentially leading to lower inbox placement and increased spam classifications.
- Skepticism for Large Senders: Conversely, some highly experienced deliverability professionals express deep skepticism that hourly fluctuations significantly impact deliverability for high-volume, legitimate campaigns. They argue that factors like overall daily volume consistency, sender reputation, and recipient engagement are far more critical.
- Reputation is Paramount: Regardless of differing opinions on hourly fluctuations, there's universal agreement that maintaining a strong sender reputation through consistent daily volume, proper list acquisition, and high recipient engagement is paramount for achieving good deliverability.
- Possible Misinterpretation: The advice regarding hourly tapering might be a misinterpretation of older IP warm-up guidelines or practices primarily applicable to less-than-truly-opt-in email streams, rather than general best practices for modern, permission-based email marketing.
Key considerations
- Overall Daily Volume: For large email campaigns, focus more on maintaining a stable daily sending volume rather than overly granular hourly adjustments. Minor intra-day fluctuations are often less impactful than significant overall daily deviations.
- Sender Trust and Engagement: Prioritize building and preserving sender trust through legitimate list acquisition, high user engagement, and good sending practices. These foundational elements typically outweigh minor hourly volume shifts for deliverability.
- Context of Advice: Evaluate the source and applicability of advice on hourly tapering. Some experts suggest this concern might be outdated or relevant specifically to cold email, co-registration, or other less-than-ideal sending scenarios, not standard, permission-based marketing.
- ISP Perception: While many experts are skeptical of its impact, documentation from major ESPs and postmaster tools indicates that ISPs do factor sending pattern consistency into their algorithms. Unpredictable hourly changes could theoretically flag your behavior as suspicious.
What email marketers say
15 marketer opinions
While some leading email platforms and deliverability firms caution that widely fluctuating hourly email send volumes within a large campaign can negatively impact deliverability by signaling suspicious behavior to ISPs, a consensus among many veteran deliverability experts on community forums suggests otherwise. For established, high-volume senders, they often deem such granular hourly tapering advice as an overcomplication, a misinterpretation of old warm-up strategies, or simply incorrect. These experts generally argue that overall daily send consistency, a strong sender reputation built on consistent engagement, and legitimate acquisition practices are far more influential on deliverability than minute hourly volume adjustments.
Key opinions
- ISP Consistency Preference: A significant number of email service providers and deliverability experts assert that ISPs prefer consistent sending patterns. Unpredictable hourly fluctuations within large campaigns can appear abnormal, potentially leading to increased spam classifications and throttling.
- Skepticism from Experts: Many seasoned deliverability professionals, particularly within community discussions, express deep skepticism or outright dismiss the advice about tapering hourly email volume for large, established senders. They often label it as 'bad' or 'nonsensical,' arguing it's an outdated or misinterpreted concept.
- Focus on Broader Factors: Experts from both sides implicitly agree that overall daily sending volume consistency, general sender reputation, proper list acquisition, and high recipient engagement are the primary drivers of deliverability, far outweighing the impact of minor hourly variations.
- Misinterpretation of Warm-up Advice: The theory of hourly volume tapering might be a misinterpretation of older IP warm-up advice, which focused on gradual volume increases, or historical limitations of past email infrastructure, rather than a general rule for ongoing high-volume sending.
Key considerations
- Prioritize Daily Consistency: Rather than obsessing over hourly fluctuations, marketers managing large campaigns should prioritize maintaining a stable and predictable daily sending volume to build and sustain a positive sender reputation with ISPs.
- Reputation and Engagement First: Strong sender reputation, built through consistent high engagement rates and legitimate list acquisition, provides a substantial buffer against minor technical nuances like hourly volume shifts. Focus efforts here before granular optimizations.
- Context Matters for Granular Advice: Evaluate the context of advice suggesting hourly volume control. For established, high-volume senders with clean lists, such advice is often deemed irrelevant or overly cautious, possibly stemming from scenarios involving less-than-ideal sending practices.
- Hourly Sending vs. ISP Ingestion: A sender's hourly volume does not necessarily equate to the volume accepted by recipient servers in the same hour. ISPs often throttle or queue emails, managing the ingestion rate on their end regardless of the sender's outbound pace.
Marketer view
Marketer from Email Geeks explains that he has not seen evidence of intra-day fluctuations in email volume significantly impacting deliverability. He notes that volume spikes relative to typical sending volume are usually more critical than hour-to-hour differences. He also suggests that this advice might be a misinterpretation of old warm-up advice and that scheduling sends at slightly off-the-hour times (e.g., 11:12 vs. 11:00) might help avoid congestion with mailbox providers. He finds it difficult to conceive a scenario where such granular advice makes sense.
31 May 2023 - Email Geeks
Marketer view
Marketer from Email Geeks expresses deep skepticism regarding the advice about tapering email volume, calling it overcomplicated at best and completely wrong at worst. She highlights that a daily send volume of 1M should easily accommodate smaller sends, and that this theory is contradicted by the simultaneous sending of triggered communications alongside bulk emails. She emphasizes that key factors for deliverability are general sending practices and engagement, typical send volume (avoiding major lulls or sporadic inflation/deflation), sending reputation (dedicated vs. shared IP), and acquisition practices focused on engaged recipients. She adds that even for warm-ups, sending consistent, highly engaged triggered communications is beneficial and the advice seems nonsensical.
16 Mar 2022 - Email Geeks
What the experts say
3 expert opinions
For large email campaigns, the impact of fluctuating hourly send volume on deliverability draws divergent views among experts. While some specialists assert that maintaining a consistent daily sending rate, including stable hourly patterns, is crucial for positive mailbox provider perception and overall sender reputation, others strongly dismiss the notion that hourly fluctuations matter for genuine, opted-in mail. The latter group contends that receiving systems primarily observe the volume directed to them and cannot discern a sender's broader hourly variations across all domains. This suggests that advice about hourly consistency may be more relevant for less-than-opt-in or cold email strategies rather than established, permission-based sending.
Key opinions
- Conflicting Expert Views: Opinions are sharply divided, with some experts emphasizing the need for consistent hourly send rates for good deliverability, while others deem it irrelevant for legitimate, opt-in campaigns.
- ISP Perception of Consistency: Some deliverability experts believe that mailbox providers prefer stable sending patterns and may view significant hourly fluctuations as suspicious, potentially impacting sender reputation and deliverability.
- Receiver's Limited View: Conversely, other experts argue that receiving systems only see the volume of mail directed to their specific domains and cannot track a sender's overall hourly volume distribution across multiple MX records, making hourly micro-fluctuations negligible.
- Context of Sending: The relevance of hourly volume consistency appears to depend on the type of email being sent; it's often advised for cold or less-than-truly-opt-in mail but dismissed for genuine, permission-based marketing.
Key considerations
- Audience Legitimacy: Prioritize sending to genuinely opted-in audiences, as this foundation often negates the need for micro-management of hourly sending volumes according to some experts.
- Overall Daily Consistency: Regardless of hourly patterns, focusing on a stable and predictable daily sending volume remains a widely accepted best practice for maintaining a strong sender reputation.
- ISP's Perspective: Understand that mailbox providers are primarily reacting to the mail they receive directly, and their algorithms may not account for a sender's total hourly output across all domains.
- Relevance of Advice: Critically evaluate advice on hourly volume tapering, as it may be more applicable to specific, less-than-ideal sending scenarios, such as cold outreach, rather than general email marketing.
Expert view
Expert from Email Geeks explains that the advice regarding email volume tapering sounds like practices seen in cold email or less-than-truly-opt-in email (e.g., co-reg, affiliate, lead gen), often focused on Yahoo. While there might be evidence it works for such mail, it is unnecessary for genuine opt-in mail. Upon re-evaluating, she strongly dismisses the advice, stating it is 'utter bullshit.' She clarifies that unless mail is specifically segmented and balanced by MX records, receiving systems only see the volume directed to them and cannot discern the overall hourly sending volume from the sender across all MXs.
11 Sep 2023 - Email Geeks
Expert view
Expert from Spam Resource explains that maintaining a consistent daily sending rate from an IP address is significantly better for deliverability than sending at widely fluctuating rates. This implies that fluctuating hourly email send volume within a large campaign can negatively impact how mailbox providers perceive sending behavior, even if the overall campaign volume is high.
18 May 2022 - Spam Resource
What the documentation says
5 technical articles
All major email platforms and industry organizations agree that fluctuating hourly email send volume within a large campaign negatively impacts deliverability. Documentation from SendGrid, Google Postmaster Tools, Amazon SES, Outlook.com Postmaster, and M3AAWG consistently emphasizes that maintaining a stable, predictable sending rate and volume is crucial for building a strong sender reputation and ensuring reliable inbox placement. They assert that Internet Service Providers (ISPs) favor consistent sending patterns, viewing erratic or sudden hourly fluctuations as potentially suspicious, which can lead to reduced deliverability and a damaged reputation.
Key findings
- Unified View on Consistency: Leading email service providers and industry bodies, including SendGrid, Google Postmaster Tools, Amazon SES, Outlook.com Postmaster, and M3AAWG, consistently advise that maintaining stable and predictable sending volumes, even hourly, is crucial for strong deliverability.
- ISP Preference for Stability: There is a clear consensus that Internet Service Providers (ISPs) prefer predictable sending patterns. Erratic or rapid hourly changes in email volume are often seen as suspicious or atypical behavior.
- Negative Impact on Reputation: Fluctuating hourly send volumes can negatively affect sender reputation. Sudden, large changes can signal instability or unreliability to receiving servers, potentially leading to increased spam classifications or throttling.
- Crucial for Trust: Maintaining a consistent sending behavior is identified as a key indicator of legitimacy for recipient servers, fostering trust and improving inbox placement for large campaigns.
Key considerations
- Maintain Predictable Patterns: To build and preserve a strong sender reputation, consistently maintain predictable hourly sending patterns within large campaigns. Avoid sudden spikes or drops in volume.
- Prioritize Consistency: Regard consistent sending rates and volumes as a core best practice. This stability signals legitimacy and trustworthiness to Internet Service Providers (ISPs).
- Impact on Reputation: Recognize that erratic hourly fluctuations can be perceived negatively by ISPs, potentially leading to adverse effects on your sender reputation and subsequent deliverability.
Technical article
Documentation from SendGrid emphasizes that maintaining a consistent and gradually increasing sending volume is crucial for building a strong sender reputation with ISPs. Rapid or large hourly fluctuations in email volume, rather than controlled growth, can negatively impact deliverability as ISPs prefer predictable sending patterns.
21 Jan 2022 - SendGrid Documentation
Technical article
Documentation from Google Postmaster Tools advises bulk senders to maintain consistent sending volume. While not explicitly addressing hourly fluctuations, the guidelines imply that erratic or sudden changes in sending patterns can negatively affect sender reputation and deliverability to Gmail users, as ISPs prefer predictable and stable sending behavior.
23 Feb 2023 - Google Postmaster Tools
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