SMTP AUTH client submission error

William Dias 1

We use SMTP AUTH client submission to send emails from our application, some emails are not sent with an error "Failure to send email" is there anyway i can retry sending of email messages which have failed.

Emily Hua-MSFT 27,526 Reputation points

2021-10-27T08:44:19.703+00:00

@William Dias
According to your description, I have 2 questions as following. Thanks for your understanding.
Are you using Exchange online?
Besides, do you refer to the steps in article "How to set up a multifunction device or application to send email using Microsoft 365 or Office 365" to set your application for sending emails?
William Dias 1 Reputation point

2021-10-27T08:54:43.043+00:00

@Emily Hua-MSFT Thank you for your responce.
We are using Microsoft 365 cloud email service for email. also we have configured sending email as per the article you mentioned and the emails send just fine.

the issue is some mails are not sent with an error "failure to send email" . these emails now do not get sent and are dropped. i would like to configure some sort of queue where failed message are tried and resent after a short duration.
Emily Hua-MSFT 27,526 Reputation points

2021-10-28T00:59:17.143+00:00

@William Dias
Thanks for your explanation,
To better help you, I would modify the tag related to Exchange online. Thanks for your understanding.
Kael Yao-MSFT 37,491 Reputation points Microsoft Vendor

2021-10-28T02:59:58.517+00:00

Hi @William Dias

I think the point here is to figure out why the message was rejected.
Was it rejected by Exchange Online or by the recipient?

Can you get some more detailed information in the application?
Kael Yao-MSFT 37,491 Reputation points Microsoft Vendor

2021-11-02T09:31:21.617+00:00

Hi @William Dias

I am writing here to confirm with you how thing going now?
If you need further help, please provide more detailed information, so that we can give more appropriate suggestions.
William Dias 1 Reputation point

2021-11-03T07:36:17.28+00:00

The rejected mails are not available in Microsoft server logs. i cannot find them when i try the trace option available in Microsoft 365. hence i can say that the issue is when application authenticates via Microsoft SMTP AUTH, most emails are sent but few are not. the application captures the error as "failure sending email" .
i read that there is a limit of 30 email per minute for sending emails on Microsoft 365. our application sends around 5 to 8 emails per minute to distribution lists created in Microsoft. each distribution list consists of 10 to 15 email ids. Microsoft also says email sent to distribution list created at Microsoft 365 is considered as 1 email.

I am at loss of ideas here.
Kael Yao-MSFT 37,491 Reputation points Microsoft Vendor

2021-11-05T06:25:12.55+00:00

Hi,
Thanks for the update.

Does this issue always occur when you have already sent a certain amount of emails?
If it is the case, I think the cause should be you have reached other limits in Microsoft 365.
For example, you may only send to up to 10000 recipients per day.
More information about the limits can be found in this link: Exchange Online limits

And do the emails which failed to be sent have something in common?
For example, with attachments.