Outlook and Microsoft 365 impose strict limits on email sending to protect their servers from spam and abuse.
These quotas quickly become blocking when you use mail merge or bulk email sending.
Microsoft 365 and Outlook impose several types of limits on email sending: number of messages per day, number of recipients per message, and sending speed (throttling).
These restrictions vary depending on the configuration, but they are designed to prevent mass email sending from a personal or business mailbox.
An Outlook mailbox can only send a limited number of emails per day. Once the limit is reached, sending is temporarily blocked.
Each email is limited in the number of recipients (To, CC, BCC), which makes large-scale campaigns more difficult.
Microsoft automatically slows down sending if too many emails are sent in a short period of time.
Bulk sends from Outlook can be detected as spam and lead to temporary blocks.
You can find these limits in detail in the official Microsoft documentation
Outlook mail merge consists of sending a personalized email to a contact list, often imported from Excel.
Even if each email is individual, the sending is still perceived by Microsoft as bulk distribution activity. This quickly triggers limiting mechanisms.
• Sending too fast: dozens or hundreds of emails are sent within seconds
• High total volume: campaigns quickly exceed daily quotas
• Automated behavior: similar to an email marketing tool
• Risk of blocking: temporary sending suspension or slowdown
A common approach is to space out sends to stay below the limits imposed by Microsoft 365.
This helps maintain good deliverability and avoid temporary blocks on your mailbox.
Tempo lets you send personalized emails from Outlook and Excel while respecting sending limits.
Instead of sending all emails at once, sends are automatically spread over time to avoid blocks related to Microsoft 365 quotas.
Immediate bulk sending → risk of exceeding Outlook quotas
Progressive and controlled sending → respects Microsoft 365 sending limits
In addition, we created a the most native integration possible without a plugin using Headless mode
Schedule your sends and stay in control of your email campaigns.
Try Tempo for free