We have just started to occasionally do mail merges to bulk emails. Each document contains custom information for the customer. These are not marketing email. Typically a run will be between 100 and 400 emails to 100-400 recipients (1 email to 1 recipient). As we migrate into Office365 is there a way to ensure we don't trip over the rate limiter?
Does Word just fire off emails as fast as it can or does it work with EOL and send a 2 per second/30 per minute?
I would advise against sending such messages through O365 - even if you don't hit any rate limits, the user or the entire tenant might be flagged, causing you issues. Where possible, try to use any of the third-party tools that specialize in mass mailings, for the numbers you are discussing you should be able to find enough free options.