Disclaimer

The information provided in this article is based on our research and publicly available Google documentation available at the time of writing. Gmail sending limits, behaviors, restrictions, and quota handling are controlled by Google and may change without prior notice.

We strongly recommend reviewing Google’s official documentation to better understand how these limits and behaviors may apply to your organization’s specific usage, configuration, and operational needs.

Overview

FBM currently uses Gmail (via SMTP) for sending reservation email notifications.

Google enforces sending limits on Gmail accounts to prevent spam and abuse. During testing and implementation review, we clarified how Gmail’s daily sending limit actually behaves.

This document explains:

• How the Gmail sending limit works

• How quota refreshes over time

• How this impacts queued email behavior in FBM

Gmail Sending Limit

For standard Gmail accounts:

• Daily sending limit: 500 recipients per rolling 24-hour period

Google Workspace accounts may have higher limits depending on the subscription type.

Official Google documentation: Gmail sending limits in Google Workspace | Google Workspace Help

Important Clarification

The Gmail sending limit does NOT reset:

• at midnight

• at the start/end of a calendar day

• at a fixed timezone-based schedule

Instead, Gmail uses a: Rolling 24-Hour Window

This means Gmail continuously checks:

“How many emails were successfully sent within the last 24 hours?”

How the Rolling Window Works

Each successfully sent email “frees up” exactly 24 hours after it was originally sent.

Example:

This means the available quota gradually replenishes throughout the day.

Example Scenario

Day 1

Totals emails sent: 500 

At this point:

• Gmail sending limit is reached
• additional emails will fail

Day 2

At 8:59 PM

500 emails sent within the last 24 hours

Sending remains blocked.

At 9:00 PM

The original 300 emails sent at:

Day 1 - 9:00 PM

are now outside the rolling 24 - hour window.

Result: 300 sending slots becomes available again

Additional emails may now be sent.

At 10:00 PM

Another: 100 slots

become available again.

Important Note About Failed Emails

Failed email attempts do NOT reset the rolling window.

Example:

Quota refresh timing is still based on:

9:00 PM successful send

NOT:

9:15 PM failed attempts

This means failed sends do not move or extend the quota refresh window.

Impact on FBM Queue Behavior

Since Gmail quota replenishes gradually:

• queued emails may begin sending progressively throughout the day

• emails do not necessarily wait for a single “daily reset”

• available sending capacity increases over time as older sent emails leave the 24-hour window

Key Takeaways

Gmail Limit Behavior

• Gmail uses a rolling 24-hour sending limit

• There is no fixed daily reset time

• Quota replenishes continuously over time

Quota Recovery

• Successfully sent emails free up exactly 24 hours later

• Failed attempts do not reset or extend the quota window

Practical Impact

• Sending availability gradually returns throughout the day

• Queue systems should expect progressive quota recovery rather than a full reset at midnight

Reference

Official Google Documentation

Gmail sending limits in Google Workspace | Google Workspace Help