Issues with Sending Bulk Emails to Gmail Users via Outlook

Question

Dear Support Team,

I am currently using Outlook to send emails to Gmail users, but the emails are being blocked.

1. Could you please confirm the maximum number of recipients I can send to at once?
2. If there are sending limits, is it possible to request an exemption?
3. Are there any recommended practices for sending bulk emails from a personal/company account?

I would appreciate your prompt assistance. Thank you!

Best regards, Hyojeong.

Answer 1

Hi @Kwak, HyoJeong ,

Welcome to our forum!

Based on your question, I have done some research and here is my answer:

Maximum Number of Recipients:

For most Microsoft 365 subscriptions, the maximum number of recipients per email is 500

The daily recipient limit is 10,000.

Requesting Exemptions for Sending Limits:  

Try these tips in this article: How can I increase sending limits?

Best Practices for Sending Bulk Emails:

• Warm-up your IP address: To establish a good sender reputation, start by sending a low volume of emails and gradually increase the count as you establish a pattern of safe and wanted emails.
• Segment Your Email List: Group your recipients based on common characteristics to send more targeted emails.

I hope this information helps!

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Answer 2

Thank you for your response.

However, I encountered an issue when sending an email to approximately 20 recipients using Gmail—it was not successfully delivered. The same issue also occurred for recipients who have been using Outlook email for a long time. Additionally, I received an email containing the following message.

'Remote server returned '550 5.4.300 Message expired -> 421 4.7.28 Gmail has detected an unusual rate of mail originating from your DKIM;domain [kiyoon.onmicrosoft.com 36]. To protect our users from;spam, mail sent from your domain has been temporarily rate limited.;For more information, go to; https://support.google.com/mail/?p=UnsolicitedRateLimitError to;review our Bulk Email Senders Guidelines. e9e14a558f8ab-3d43b57ba95si2840185ab.98 - gsmtp''

Could you kindly clarify what the issue might be and suggest possible solutions to resolve it? I would greatly appreciate your guidance.

Answer 3

Hi @Kwak, HyoJeong ,

Are you using Exchange Online or Outlook.com as your email service?

From the NDR message the issue is with backend.

If possible, please contact Microsoft support for further investigation.

Exchange Online: contact the global administrator in your organization to open a service request in Microsoft 365 admin center>Support>Help & Support.

Outlook.com: How to get support for Outlook.com

Thanks for your understanding.

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