Thanks for the reply. We are currently using version 10.38 of NetTalk.
Ok, did another run with /nettalklog on. In the log there is a _DebugPacketNumber value, which is incrementing and value "data length" which seems to quite constantly be 4096. Can total downloaded bytes be calculated by multiplying the two values together? If so, the download seems to stop before the full message is received, in the case of the log there is about 23 MB downloaded on a message than has 27 MB attachment.