Email sends, lower performance the greater the batch?

[Anonymous]

Wh have a pretty large database, and in our regular nurture emails, we send to different groups of people. Often when a send has over 15k people in it, we see that there is a much lower open/click performance versus the same send with about 5k people in it. 

Are there any best practices on how many people should be included in a batch send to optimize performance?

[Nichole_Cunnin4]

More targeted lists generally perform better. I've noticed our performance dropping a little lately for larger emails sends. Marketo does their own staggering of emails, but I like to put an extra stagger step in as a safety percaution.

I usually do batches about 30 minutes apart, which seems to help with deliverability. I aim for around 15K per batch, but I'm curious to hear from other folks in the Marketo Community too. 

[Michelle_Tizian]

Our lists are usually targeted, but when it's over 10k, I tend to split the list and run A/B or multivariate tests.

[Edward_Masson]

You really can't compare the performance of a large list with a small list. You want apples to apples comparison.
Like Michelle, you've got to break that large list down by finding some way to segment it.