You should always relate your email campaigns to users who are on-topic (segmenting your list as much as possible is advised. i.e. we wouldn't send an email campaign about Cloud features to our self-hosted clients 🙂 ), who are recently active with your campaigns, and obviously, those who know who you are still.
From a technical perspective, yes, there are huge risks sending a bulk email of that size in one go. If you're sending to email addresses from users who haven't been on the community for a while, your email sending provider will likely block you once you get a lot of bounce backs if those addresses don't exist or otherwise. If they your provider doesn't, the recipients' email provider could also blacklist your domain or sending IP address. If the receiving individual doesn't recognize who you are either, they could more than likely report you as spam too. Which will also hurt you.
Due to this, I would suggest reviewing your list criteria and make sure you're communicating with individuals who are relevant to your topic, who are active-ish on your community, and obviously, would want to receive such an email.
Another example is if you are sending an email out to advertise maybe an event which only has 30 seats, you don't want to send an email to 100k individuals in one go. People will get mad if it fills up right away. Best to send out in batches or get your criteria as specific as possible to those who would most likely benefit most from the event and then move on from there.