I've figured out what the issue is

Notes/Domino 8 Forum

Subject:

If the original mail delivered to Domino does not have a MIME-Version header (as is the case for messages sent from a Unix /usr/bin/mail which includes most Unix-based web applications like Bugzilla), Domino adds one when your client requests the message via IMAP. However, Domino does not increment its count of bytes in the message to match. As a result, it tells the client in the IMAP response "I'm about to send you X bytes", then sends 19 bytes more than that (MIME-Version: 1.0<CRLF>). The client sees this and explodes.

This affects messages that came across from Domino 7 as well as new messages delivered to Domino 8.

This doesn't affect Thunderbird because for whatever reason its IMAP implementation ignores the byte count sent by the server, opting instead to look for the "end of response" marker.

I have PMR #57636 215 616 open with Lotus support at the moment to try and get a fix for this issue sorted out.

Feedback response number WEBB7GMV3A created by ~Ben Reboosisterynds on 07/17/2008