Overview

You are experiencing an issue with messages stuck within the message queue with a status of “541 4.4.4 Temporary Server Error” for messages to O365 users. This issue impacts all users on your mail server when emailing these particular recipients.

Solution

This particular SMTP response and status code combination are most often received from O365 when the receiving server is intentionally blocking the connection. Commonly this occurs when they have blacklisted/greylisted your IP address or when throttling connections from your server in response to bulk emails as a spam deterrent.

As this can appear for a number of reasons, you can use the steps below to help verify the cause and alleviate any potential issues within your control.

1. Verify no connection issues via the SMTP Debug logs:
   1. Navigate to WebAdmin > Logs > Debug.
   2. Right-click and select Messages.
   3. Enable the SMTP Client, SMTP Server, and Queue Processing Debug Messages.
   4. Send a Test email to the affected domain to generate SMTP Conversation logs.
   5. Analyze the Debug Log entries and isolate where within the SMTP Conversation the issue appears to confirm that the connection issue is appearing directly from the recipient end. 
      1. Example of a common sequence for this SMTP Error showing a successful initial connection with the failure appearing when attempting to send the MAIL Command:
         
         
      2. This indicates that the issue is not a fault with the Kerio Connect Server’s ability to connect, but rather a rejection on the recipient server’s end.
2. If the recipient is a regular contact point, contact them directly to request that your IP be whitelisted on their end.
   1. By whitelisting your IP, you can potentially prevent further greylisting scenarios.
3. Verify the connectivity between your SMTP server and the O365 server using Microsoft’s Remote Connectivity Analyzer to perform an Outbound SMTP Test.
   1. This can often help illuminate unexpected record-specific issues in your configuration that might lead to temporary rejections.
4. Check your Domain against blacklists using a 3rd-party utility like mxToolbox.
   1. This can quickly help rule out this as a cause for the trouble. If you identify your IP within any Blacklist, you can contact the identified authority directly to investigate what steps can be taken.
      1. In some cases, it may be preferred to contact your ISP to investigate your options.
   2. You can use Microsoft’s Support Request form to request a delisting from their internal blacklists.
   3. To help prevent your domain from being incorrectly blacklisted in the first place, see Preventing Your Emails from Being Marked as Spam.

Testing

After taking steps to address the identified issues (whitelisting your IP on the recipient end, removal from any blacklists, or identified DNS record issues fixed) you should no longer encounter issues connecting to the target domain.