NM: ! Error: BTNotesMIMEProcessPart: BTNotesMIMEPrintPartData - (1205) MIME part truncated. (4315685)

Issue

What is causing this migration error?  I found this in the migration logs for some users

! Error: Notes error code: 1205 (hex 000004b5)
! Error: Failed to open document: (1205) MIME part truncated.
! Error: Notes error code: 1205 (hex 000004b5)
! Error: BTNotesMIMEPrintPartData: MIMEGetEntityData - (1205) MIME part truncated.
! Error: BTNotesMIMEProcessPart: BTNotesMIMEPrintPartData - (1205) MIME part truncated.
! Error: BTNotesMIMEProcessPart: BTNotesMIMEProcessPart - (1205) MIME part truncated.
! Error: BTNotesMIMEProcessPart: BTNotesMIMEProcessPart - (1205) MIME part truncated.
! Error: BTNotesMIMEPrintPartData: MIMEGetEntityData - (1205) MIME part truncated.


Reason

This error indicates Domino may have truncated the messages which is usually due to either archiving (with the option to truncate rather than completely move documents) or a replication formula which specifies the size of messages during replication.
In this case it is likely to be due to a replication formula as these would be assumed to be relatively new emails / calendar items.
Validate the replication settings on the primary mail file for the section under "To shorten all documents or limit attachments you receive in a replica". It may be that this mail file was originally set to use the truncation method so is not replicating full documents for migration.

Also ensure there's no archive policy which may be including the email documents.
Additionally it would be good to ensure the source mail file has a standard mail template applied. To do this, you can run the below Domino console command against the mail file.

Load convert -u mail\mailfilename.nsf * standardmailtemplate.ntf

The ntf would be the current IBM Domino version for the environment, eg mail85.ntf