Error code 0x7da
: From a support forum: "The error means "ecMessageNotRenderable". Emails in Exchange Information Store can be saved in Rich Text format, which is the format used in MAPI. In order to be transferred via POP3/IMAP4, the email should be converted to MIME. In case Exchange failed to render the message into the RFC822 standard for Internet text messages, the error 1023 with code 0x7da will be logged in application log.
Please kindly refer to the ME329168
article for this issue: Error When You Open a Message with a POP3 E-Mail Client
Theoretically we can remove the problematic item in the user's mailbox to eliminate this error. However, it's not easy to locate the message with the ID 0001-0000001cded6. In this condition, I suggest we try to fix this issue by moving the user's mailbox to another Mailbox store (store in different storage group preferred). During mailbox move, Exchange will scan all items in the mailbox and remove any corrupted one.
After moved the mailbox, please ask the user to access mailbox and check if the error disappeared. If the issue persists, please try to exam the entire mailbox store with utility Isinteg. Isinteg is a tool which can check an offline mailbox store and fix any integrity issue in application level.
In addition, please also refer to ME284271
regarding the issue if the above methods cannot solve the issue: POP3SRV Event ID 1023 with Multiple Services in Profile.