Based on aggregate Mailblast campaign data since 2023, send-time data shows clear patterns: Friday is the best day for engagement at 22.2% aggregate open rate, Saturday is the worst at 13.0%, and 8 AM UTC is the peak hour at 24.9%. The "send Tuesday-Wednesday" advice that dominates email marketing folklore is correct for sender volume but not for engagement. Wednesday gets the most sends in the data, but Friday gets the best engagement.
This post walks through the day-of-week and hour-of-day open-rate patterns, the AWS region context that shapes them, and what they actually mean for choosing a send time. All numbers use the campaign's scheduled send time rather than per-recipient delivery time, so the analysis reflects sender behavior rather than recipient receiving patterns.
What Day of Week Produces the Best Open Rate?
Friday produces the highest aggregate open rate at 22.2% across the Amazon SES data, followed by Tuesday at 19.4%. Wednesday and Thursday cluster in the 17.0-17.5% band. Saturday is the lowest at 13.0%. The pattern is driven by a combination of sender selection (which campaigns get sent on which days) and recipient behavior (when people actually open email). Both effects push in the same direction: weekday mornings produce stronger engagement than weekends.
| Day of week | Open rate | Click rate |
|---|---|---|
| Monday | 16.71% | 0.38% |
| Tuesday | 19.38% | 0.57% |
| Wednesday | 17.47% | 0.53% |
| Thursday | 17.04% | 0.48% |
| Friday | 22.20% | 0.61% |
| Saturday | 12.96% | 0.43% |
| Sunday | 16.83% | 0.57% |
The Wednesday volume vs Friday engagement split is the most useful observation in the data. Wednesday gets sent noticeably more than Friday, but Friday's open rate is 4.7 points higher. The folk wisdom that "Tuesday-Wednesday is the best time to send" reflects what senders actually do, not what produces the best engagement. The senders sending on Wednesday are competing against more inbox noise. The senders sending on Friday are reaching emptier inboxes.
What Hour of the Day Produces the Best Open Rate?
The peak engagement hour is 8 AM UTC at 24.9% open rate. The 7 AM to 9 AM UTC window broadly outperforms other times: 7 AM is 20.7%, 8 AM is 24.9%, 9 AM is 20.5%. The pattern reflects a sender population that skews European, with a large share of accounts configured in AWS's Ireland (eu-west-1) region. 8 AM UTC is the start of the European working day. US-focused senders see equivalent relative effects shifted to morning local time, though the data here aggregates everyone into UTC.
A second pattern in the hourly data: the "popular" hours (11 AM to 1 PM UTC) underperform the earlier morning hours by 2-7 percentage points. Senders crowd the late-morning slot because it is marketing folklore that 10-12 is the "best time to send," but at scale this means competing for inbox attention with everyone else following the same advice. The earlier 7-9 AM UTC window is less crowded and produces better engagement: 8 AM averages 24.9% open rate against 17.9% at 11 AM.
Why the Data Looks This Way
Two effects compound across both the day-of-week and hour-of-day patterns:
Recipient behavior: People actually open email during their working hours, with peaks at the start and end of the workday. The 8 AM UTC peak matches "first inbox check after waking up" for European recipients. Friday morning is especially strong because recipients are catching up on the week's email before the weekend.
Sender selection: Different sender types choose different sending times. Senders who schedule for late evenings or weekends tend to be cold-list operators or low-engagement broadcast lists. Senders who schedule for European working-morning slots tend to be B2B and professional services with engaged subscriber bases. The data doesn't distinguish these populations; it just shows what each chooses.
The practical takeaway: send-time benchmarks are useful as a starting point, but the right send time for a specific list depends on where the recipients are and what they're doing at that time. For a US-recipient list, shifting the data 5-8 hours east gives you the equivalent local windows. For a global list, the best practice is to segment by region and schedule each segment for its own local morning.
What Send Time Doesn't Affect
Bounce rate and complaint rate do not track send time in any useful way. Across the data, bounce rates during business-hour windows (5 AM to 7 PM UTC) sit in the 0.05-0.31% range; complaint rates sit in the 0.003-0.011% range. The few hours that spike higher (hour 3 UTC at 0.67% bounce, hour 4 at 0.61%) reflect sparse-sample noise from a small number of off-hours campaigns, not a fundamental rule about those hours. Send time is an engagement variable. It moves opens and clicks; it does not move the deliverability metrics that drive AWS reputation thresholds (AWS, 2026).
For senders trying to fix deliverability issues, send-time optimization is the wrong place to look. The deliverability levers are list hygiene, authentication, and reputation. See the list size vs deliverability data for the volume tier that produces the lowest bounce rates.
What This Means Operationally
The cohort-level patterns suggest four working defaults for choosing an Amazon SES send time. Aggregate patterns describe the typical campaign in the dataset, but the right send time for a specific list still requires per-list testing. Treat the numbers below as a starting hypothesis, not a final answer.
- Send Friday morning for marketing email if your audience and content fit. The 22.2% aggregate open rate on Friday is roughly 27% higher than the 17.0-17.5% mid-week baseline.
- Avoid Saturday unless your content is specifically a weekend-relevant broadcast. The 13.0% aggregate Saturday open rate is 9 points worse than the best weekday and 4 points worse than the next-worst day.
- Send earlier in the morning than the conventional 10-11 AM slot. The 7-9 AM UTC window is less crowded and produces better engagement for European-skewed lists. Shift to local morning for other recipient geographies.
- Stop reasoning about deliverability at send time. Bounce and complaint rates do not move meaningfully with timing; they are driven by list quality and authentication, not the hour on the clock.
FAQ
What is the best day to send marketing emails?
Based on aggregate Mailblast campaign data since 2023, Friday produces the highest aggregate open rate (22.2%), followed by Tuesday (19.4%). Saturday is the worst day at 13.0%. The "best day to send" widely cited in marketing folklore (often Tuesday-Wednesday) is correct for volume but not for engagement: the data shows Friday wins on engagement at scale.
What time of day should I send marketing emails?
The peak engagement hour across our Amazon SES data is 8 AM UTC, which produces a 24.9% open rate. The 7-9 AM UTC window broadly outperforms other times. This reflects a sender population that skews European, with a large share of accounts configured in AWS's Ireland (eu-west-1) region, and 8 AM UTC is the start of the European working day. For US-focused senders, equivalent local times produce similar relative effects.
When do people send the most marketing emails?
Volume concentrates Tuesday through Friday between 11 AM and 1 PM UTC. The single highest-volume slot across the data is Sunday 11 AM UTC, reflecting weekend broadcast campaigns timed for the European Sunday afternoon. High-volume slots don't correlate with high-engagement slots: the popular 11 AM UTC slot averages 17.9% open rate, while the less-crowded 8 AM UTC slot averages 24.9%.
Does send time affect bounce rate?
Not meaningfully. Bounce rate is determined by list quality (whether the address is valid), not by what time the message is sent. Across the data, bounce rate variance by hour and day is statistically noise. Send time affects engagement (opens, clicks); it does not affect deliverability (bounces, complaints). Focus send-time optimization on engagement, not deliverability.
Why do some hours have much higher open rates than others?
Two effects compound. First, time-of-day correlates with when recipients check email: business hours in the recipient's timezone produce higher open rates. Second, sender selection: senders who send at unusual times (like 4 AM UTC) tend to be cold-list operators with lower-engagement audiences. The 4 AM UTC dip in the data (9.8% open rate) reflects both effects, not a fundamental rule about that hour.
How Mailblast Fits
Mailblast schedules Amazon SES campaigns in any UTC slot you choose and reports per-campaign open, click, bounce, and complaint rates back from your own AWS account. The platform is the management layer on top of your SES, so timing decisions, list segmentation, and analytics all live in one place while the actual delivery and reputation run through your AWS keys. Drag-and-drop editing is powered by BeeFree; analytics ship on every plan including the free tier (1,000 contacts, 10,000 emails per month, "Sent with Mailblast" footer). Automation and unbranded sending start on the first paid rung, $10 per month for that same 1,000 contacts.
Methodology: aggregate open and click rates computed by day-of-week and hour-of-day of the campaign's scheduled send time, for sent and completed campaigns from 2023-01-01 to present. The hourly breakdown is limited to campaigns with at least 1,000 recipients to reduce small-sample noise. Accounts with aggregate bounce rates at or above 3% are excluded as not representative of standard deliverability. Volume-weighted figures. UTC timezone. Recipient timezone unknown; recipient-side local-time effects are approximate.
Disclosure: Mailblast is a hosted email marketing platform built on top of customers' own Amazon SES accounts. This post analyzes aggregate, anonymized data from Mailblast-managed campaigns and is published by the Mailblast team.