No X-UIDL header found

The following mailman methods use the X-UIDL email header as the means to identify the email to be downloaded or deleted from a POP3 server:

GetFullEmail
DeleteEmail
DeleteBundle

If no X-UIDL header is found within the email, then it is not possible to determine the sequence number of the email to be downloaded or deleted. (POP3 commands to fetch or delete an email require a sequence number. The sequence number is unique only to the POP3 session. The POP3 UIDL command is used to get a list of UIDLs and their corresponding sequence numbers — allowing a UIDL to be mapped to a sequence number. The methods listed above use the X-UIDL header field value to find the sequence number to be deleted.)