This article explains how sequence scheduling works with multiple inboxes.

When there are multiple inboxes connected to a sequence, the emails are assigned to each inbox in cyclic order.

Consider a sequence with 2 inboxes and 7 emails. The scheduling will be done in the following manner -

This means -

→ Emails 1,3,5,7 will be sent from inbox 1

→ Emails 2,4,6 will be sent from inbox 2

Follow-ups for respective emails will also be sent from the same inboxes.