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Delay Receiving Emails from Outlook Clients

wellington silva

Hello,

I'm experiencing an issue with receiving emails from Outlook (Microsoft) clients.

The emails from Microsoft clients are sometimes delayed by 10 to 18 minutes, and in some cases, the delay can extend to several hours.

To mitigate this, we've added firewall rules to allow Microsoft IP ranges to connect for email purposes, as follows:

# Emails Microsoft
tcp|in|d=25|s=40.92.0.0/15 # Microsoft Exchange Online
tcp|in|d=587|s=40.92.0.0/15 # Microsoft Exchange Online
tcp|in|d=465|s=40.92.0.0/15 # Microsoft Exchange Online
tcp|in|d=25|s=40.107.0.0/16 # Microsoft Exchange Online
tcp|in|d=587|s=40.107.0.0/16 # Microsoft Exchange Online
tcp|in|d=465|s=40.107.0.0/16 # Microsoft Exchange Online
tcp|in|d=25|s=52.100.0.0/14 # Microsoft Exchange Online
tcp|in|d=587|s=52.100.0.0/14 # Microsoft Exchange Online
tcp|in|d=465|s=52.100.0.0/14 # Microsoft Exchange Online
tcp|in|d=25|s=104.47.0.0/17 # Microsoft Exchange Online
tcp|in|d=587|s=104.47.0.0/17 # Microsoft Exchange Online
tcp|in|d=465|s=104.47.0.0/17 # Microsoft Exchange Online
# Emails Microsoft END

However, the problem still persists. It's also worth mentioning:

This issue is periodic — some days it occurs, other days everything works fine.

When testing, emails from Microsoft domains consistently show delays, but emails from Gmail clients arrive instantly without any issues.

If we restart the firewall, the problem is temporarily resolved, but the delays return after some time.

Does anyone have any suggestions on what else I should check? Could this be related to connection tracking, rate limits, or specific DirectAdmin settings?

Thanks in advance for any help.

Comments

3 comments

Date Votes
  • cPRex Jurassic Moderator

    Hey there!  If you check the Exim logs on the server and you don't see any delays there, the issue likely isn't on your machine but external on the network.  It's not unreasonable for it to take 10 minutes for an email to appear as it's not always instant (greylisting, spam testing, network traffic, etc.)

    You also mention DirectAdmin, but this is the cPanel Forums so I wouldn't have any knowledge of that.

    0
  • wellington silva

    We have added the relevant IP ranges to the CSF allow list to ensure traffic from Microsoft is not blocked

    0
  • cPRex Jurassic Moderator

    If adding the IPs doesn't change the behavior, but stopping the firewall briefly does change things, the IP list is either incorrect or there is something else happening with the firewall leading to the problem.

    0

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