I'd be very careful with any mass emailings unless you are using a service to send these and not just your resident SMTP server or Office365. We're had some overly ambitious salespeople do email blasts from their client and get our domain blacklisted as a spammer more than once <g>. Depending on volume, you may also risk the recipient marking your email address as 'junk', hindering your ability to reach them when you have a customer specific issue to communicate.
Just my initial IT reaction; I realize I did not address any NAV specific issue herein. We can't seem to get NAV to send to a Office365 distribution list (yet) so cannot comment on that. Maybe I'll learn something (other than Azure/BC can do it).
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