It seems no one has asked about his question. What's the best practice to send large volume of emails, like 500K or 1 millions of emails? I understand that it's not a good idea to send 500k emails in a patch. What's the max volume of emails per patch? Can I use "send using multiple wave" or use regular split, like A/B split?
It will be difficult to summarize everything in a single thread but you should definitely follow these steps
Know your contractual obligation of number of emails per hour
Check if the hardware provisioned for your instance is capable of handling this much load
Breakup your target audience against the domain like how many out of this 500k is for Gmail, Hotmail etc.
Work with a deliverability consultant to see if your MX rules cater to this requirement or not. If your instance is fairly new, the sending IPs might not have been warmed up till now and sending huge volumes can cause blacklisting or bad IP reputation.
Plan your sending audience based on MX rules otherwise if you are overquota on the rules, there will be internal throttling.
Keep the size of email small (~ 60-70K)
Check your target audience is all valid addresses and there aren't typos on the email address like domain such as gamil.com, hotmil.com
Use waves sending feature for better sending reputation.
What would my approach be if I need to send emails with a bit more inconsitent frequency? See image as reference.
Every week I send about 2000 emails of a more transactional nature (blue).
Last two weeks each month I send about 30k emails, also more transactional (red).
First week each month I send campaign email to about 30k receipients (green).
Then we have the spikes, green and purple, of about 300k receipients spread out through the year with no consistent schedule.
I am using an IP with a high Sender Score (97) and have been using that for a couple of years, so I don't expect any need for warm up to gain reputation and such. But what about cool down? Will that occur if my number of emails go down a couple of weeks, such as between weeks 20 and 26? What kind of impact will that have on my scheduled send out to 300k week 26?