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Unable to send mass emails through MS365


I have a client which uses MS365 for email.

Once per month they run reports for their clients, this results in around 2000 emails being sent out. MS365 stops them sending after a few hundred, thinking they are spamming. 

The reporting tool sends the emails through Outlook. 

How do I fix this issue?



OutlookExchangeMicrosoft 365

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David Favor

8/22/2022 - Mon

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hi Mas,

Thanks for the idea, i will give you more info.

Their CRM reporting tool creates all the billing reports for the 2000 clients at the same time each month. It then instantly emails them all to the clients. An excel spreadsheet or similar is not involved.

Can SendGrid/MailChimp, or similar, work with Outlook?
Scott Fell

Mas's solution is the way to go.

Using Sendgrid (or similar like https://www.mailgun.com/) is the way to go. What you will do is replace the outgoing smtp server info with your account for sendgrid. https://docs.sendgrid.com/for-developers/sending-email/getting-started-smtp this is very similar to using an app password with outlook.  

And the similar for Mailchimp https://mailchimp.com/developer/transactional/docs/smtp-integration/ or mailgun https://documentation.mailgun.com/en/latest/quickstart-sending.html#send-with-smtp-or-api

In addition to setting up your account for one of these options, you will also want to set up DKIM and SPF records for good deliverability. All of that will also be documented.


MAS provided a very useful link about the limits with O365.  It appears that you can send 30 messages every minute without causing you to get blocked.  Is it possible for you to do some scheduling in your reporting tool?  You could send them all if you spaced them out over about 80 minutes.
Your help has saved me hundreds of hours of internet surfing.
Scott Fell

While you could potentially send mail in spurts of 30, that would mean your crm can handle that. However, it is not a good idea to send bulk email through your email account like this. The third party options are set up for this.  Overall, it helps your deliverability of your bulk mail through the bulk mail provider and not put your main email in jeopardy. 
Vasil Michev (MVP)

I'd add my voice to the recommendations above - while the limits allow for sending few thousand messages, doing so will likely result in the account getting temporary blocked. Repeated offenses can also result in the entire tenant being blocked. So best consider using a third-party service that specializes with bulk sending, or use some appliance in your on-premises environment.
David Favor

This relates to the outgoing SMTP Relay you're using, either your native MTA, MS365, https://smtp2go.com or any other Relay Service.

The dirt simple fix will be to just use https://smtp2go.com which provides 1st 1000 messages/month free, so you'd only pay for 1000 message send... so a few dollars...
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