Troubleshoot delayed external emails in Alibaba Mail
Analyze email headers to identify which mail server caused a delivery delay.
Overview
When external emails arrive late, view the email source headers to pinpoint where the delay occurred.
Procedure
1. Log in to the Alibaba Mail web client, go to Inbox, select the delayed email, right-click the email body, and choose View Source.
2. Locate the Date field. The timestamp, such as Mon, 30 Nov 2020 14:57:13 +0800, indicates when the sender's client sent the email. This value may be inaccurate if the sender's clock was misconfigured, but this is rare. 
3. Find the last Received field above the Date field. If its timestamp is significantly later than the preceding Received fields, a delay occurred on that mail server.
4. Identify which Received field shows the largest time gap. The server with the longest gap caused the delay. Contact that server's ISP to investigate.
The screenshot above shows an example with no delay.
References
Receiving delays after you configure an Alibaba Mail account in a third-party client