Received notification of Undelivered Email in Workmail but recipient keep receiving duplicated email

Two Emails were sent to a recipient last night (1st mail with 11 attachments/total 5.1MB at 10:40UTC 14/07/2022 and 2nd mail with 22 attachments/total 22.1MB at 10:40UTC 14/07/2022) but I received a notification email "Undelivered Mail Returned to Sender" for the 2nd email this morning (at 01:48UTC 15/07/2022) with content below:

Technical report:

Reporting-MTA: dns; xxx.smtp-out.us-west-2.amazonses.com

Action: failed Final-Recipient: rfc822; aaa@abc.com Diagnostic-Code: smtp; 550 4.4.7 Message expired: unable to deliver in 840 minutes.<421 4.4.2 Communication interrupted> Status: 4.4.7

I tried to re-send both emails to the recipient this morning. However, the recipient has contacted me that he received 33 duplicated emails for the 2nd email I sent last night (from 10:44UTC 14/07/2022 to 01:49UTC 15/07/2022) and keep receiving my re-sent 2nd email now. It seems that amazoneses try to resend the 2nd email until 840 minutes reached. The recipient was serious affected since his mailbox was full due to my duplicated emails.

In Workmail, I cannot find the duplicated email from sent folder. I just wonder why would this happened and what should I do to prevent this issue.