IMAP-868 — The proxy cannot sent a mail in the form of literal string
The proxy wants to send mail data to the server. A literal string is used for this, i.e., a block of data prefixed by length. This message means that the line containing the literal length at the end does not fit to a buffer. You may try to enlarge buffer sizes in IMAP4-PROXY.CLIENT-CONN and IMAP4-PROXY.SERVER-CONN.