Webmethods Email port : Mails not deleted automatically after processesing

Hi Expert,

I am facing an issue with the email port functioning in Web methods.

In my project I am having to mailbox for TEST and PROD env. Both the email ports are having same configuration settings but points to different email ids.
My email port polls for the mails coming in the Inbox folder and processes the same using webM code and then deletes the mails from the Inbox folder automatically. Currently this is still occurring in TEST.
But, in PROD the mails are not getting deleted after being processed and so they remain in the Inbox as unread and is polled every time by the port and the processing repeats like an infinite loop, unless i manually delete the mails from the Inbox folder.

Following are the configuration details :
Server Information :
Type : POP3
Host Name : pod51015.outlook.com
Transport Layer Security : Implicit
Time Interval (seconds) :30
Log out after each mail check: No

Running as Admin.

Message Processing :
Send reply email with service output :No
Send reply email on error :No
Delete valid messages (IMAP only) :Yes
Delete invalid messages (IMAP only) :Yes
Multithreaded processing (IMAP only) :No
Number of threads if multithreading turned on :0
Invoke service for each part of multipart message :No
Include email headers when passing message to content handler :Yes
Email body contains URL encoded input parameters :No

Can you please advice and a provide your inputs as why suddenly I am facing this behavior in PROD , though it works perfectly in TEST.