NM: Calendar Migration Crash on MAPI Too Big Error 80040305 (4315399)

Issue

We've encountered the following error in almost every migration so far.

What is causing this issue?
! Error: Save Changes --MAPI Too Big Error 80040305
! Error: Saving Properties --MAPI Too Big Error 80040305
! Error: Open Property --Error code 8004010f
! Error: Save Changes --MAPI Too Big Error 80040305
! Error: MAPI Create Message --MAPI Too Big Error 80040305  

Solution

This is caused by a product called Vaultive, which encrypts the data at the network level.
Even though Vaultive may be turned off, it will still authenticate through the Vaultive proxy.
Vaultive must be completely removed, so the calendar items will migrate successfully without error.