Save ALL emails for reference. Occasionally send updated versions of the MSS with latest page numbering. Wipe or store elsewhere older versions. Never allow yourself to be angry or express disagreement in salty terms. Your partner will have off-days, too.
All writers are egoists.
Keep those emails on hold, sleep on them. You'll often find that your teammate was spot on after all. Trust your partner implicitly but never feel shy about double checking a statistic, historical fact, spelling etc. We can all be guilty of slips and typos. A good partner will never object to a failsafe.