emails sending extremely slow

Question

emails sending extremely slow

Rosie Lee 0

Emails seem to be taking hours to send if at all sometimes we have to retrigger them completely.

Praneeth Maddali 10,025 Reputation points Microsoft External Staff Moderator

2025-09-22T15:45:13.4966667+00:00
Hi @Rosie Lee

Thank you for reaching out regarding the slow email sending issue. To help us find the best solution for you, could you please answer these questions in simple terms?

What email system are you using? Is it Microsoft 365 (cloud), an on-premises Exchange Server, or both? If it’s Microsoft 365, do you know your plan type (Business, Enterprise, etc.)?

Which app is affected? Are the delays happening in Outlook (desktop or web), another email app, or both? If it’s Outlook on your computer, please check the version (File > Office Account > About Outlook).

Who are you emailing? Are the emails sent internally or externally? Do they include large attachments or are you sending many at once?

What exactly occurs? Are there error messages, or do emails remain in the Outbox? Are delays worse at specific times?

Any recent changes? Have you updated network settings, security software, or spam filters recently?

Have you tried testing? Please try sending an email from Outlook on the web (outlook.office.com). Is it faster than the desktop app?

Once we have this information, we can provide a targeted solution with the appropriate Microsoft documentation.
Rosie Lee 0 Reputation points

2025-09-22T15:52:04.9066667+00:00

We are using Azure Email Communication Services via SMPT sending through our CRM. But no one is sending anything more than 1000 at a time per our in house rules so that way we never hit the throttle limits. This is externally our customers, happening across the country, no changes in those offices networks or updates on our end to filters etc.
Anonymous

2025-09-22T22:21:05.8966667+00:00
Hi @Rosie Lee ,

Thank you for submitting your question on Microsoft Q&A.

It sounds like what you’re seeing is delayed or dropped email delivery through Azure Communication Services (ACS) Email over SMTP. Since this is happening sporadically, across different locations, and nothing has changed on your side, the issue could be tied to one of a few things:

Something on the Azure side, like service degradation, queuing delays, or regional throttling.

Delays on the recipient’s end, such as greylisting, spam filtering, or DNS resolution issues.

SMTP relay or connection stability problems, like timeouts, retries, or your CRM not syncing properly with ACS response codes.

To help narrow it down, here are a few checks you can try:

Look at ACS Metrics – In the Azure portal, go to Communication Services → Email → Metrics, and check the delivery attempts, failures, and throttling graphs.

Enable Advanced Logging – Turn on SMTP diagnostic logging in your CRM or ACS client app to see where delays are happening.

Trace a Sample Message – Grab the Message ID for one of the delayed emails and run a delivery trace in ACS. That will show whether it got stuck in ACS, on its way out to the recipient, or at the recipient’s server.

Check Azure Service Health – Look at the Service Health blade in Azure to see if there were any regional issues with ACS/Email during the times you noticed delays.
Anonymous

2025-09-24T01:08:57.34+00:00

Hi @Rosie Lee ,

Could you please review my comments, follow the steps, and let me know whether your issue has been resolved?

1 answer

Your answer

Praneeth Maddali 10,025 Reputation points Microsoft External Staff Moderator

2025-09-22T15:45:13.4966667+00:00

Hi @Rosie Lee

Thank you for reaching out regarding the slow email sending issue. To help us find the best solution for you, could you please answer these questions in simple terms?

What email system are you using? Is it Microsoft 365 (cloud), an on-premises Exchange Server, or both? If it’s Microsoft 365, do you know your plan type (Business, Enterprise, etc.)?

Which app is affected? Are the delays happening in Outlook (desktop or web), another email app, or both? If it’s Outlook on your computer, please check the version (File > Office Account > About Outlook).

Who are you emailing? Are the emails sent internally or externally? Do they include large attachments or are you sending many at once?

What exactly occurs? Are there error messages, or do emails remain in the Outbox? Are delays worse at specific times?

Any recent changes? Have you updated network settings, security software, or spam filters recently?

Have you tried testing? Please try sending an email from Outlook on the web (outlook.office.com). Is it faster than the desktop app?

Once we have this information, we can provide a targeted solution with the appropriate Microsoft documentation.
Rosie Lee 0 Reputation points

2025-09-22T15:52:04.9066667+00:00

We are using Azure Email Communication Services via SMPT sending through our CRM. But no one is sending anything more than 1000 at a time per our in house rules so that way we never hit the throttle limits. This is externally our customers, happening across the country, no changes in those offices networks or updates on our end to filters etc.
Anonymous

2025-09-22T22:21:05.8966667+00:00

Hi @Rosie Lee ,

Thank you for submitting your question on Microsoft Q&A.

It sounds like what you’re seeing is delayed or dropped email delivery through Azure Communication Services (ACS) Email over SMTP. Since this is happening sporadically, across different locations, and nothing has changed on your side, the issue could be tied to one of a few things:

Something on the Azure side, like service degradation, queuing delays, or regional throttling.

Delays on the recipient’s end, such as greylisting, spam filtering, or DNS resolution issues.

SMTP relay or connection stability problems, like timeouts, retries, or your CRM not syncing properly with ACS response codes.

To help narrow it down, here are a few checks you can try:

Look at ACS Metrics – In the Azure portal, go to Communication Services → Email → Metrics, and check the delivery attempts, failures, and throttling graphs.

Enable Advanced Logging – Turn on SMTP diagnostic logging in your CRM or ACS client app to see where delays are happening.

Trace a Sample Message – Grab the Message ID for one of the delayed emails and run a delivery trace in ACS. That will show whether it got stuck in ACS, on its way out to the recipient, or at the recipient’s server.

Check Azure Service Health – Look at the Service Health blade in Azure to see if there were any regional issues with ACS/Email during the times you noticed delays.
Anonymous

2025-09-24T01:08:57.34+00:00

Hi @Rosie Lee ,

Could you please review my comments, follow the steps, and let me know whether your issue has been resolved?

Answer 1

Rosie Lee 0

Again - no health issues listed. Being told we can't add SMTP logging. Looks like we will just have to deal with the lag and constant reattempts

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emails sending extremely slow

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