With Instantly you can connect unlimited accounts to send from and have up to 100 email accounts in one campaign so you do not need to create a separate campaign for each account.
You can add more sending accounts in Campaign - Option page:
Instantly will then rotate sending emails between these accounts to make it more natural.
FAQ
Q: How will my emails be sent if I have more than one email account as a sender?
A: If you have more than one account as a sender and a gap of 5 minutes, every 5 minutes you will have one email sent from each email sender.
Q: What will happen with my campaign if I remove one email sender?
A: If you remove the email account from an active campaign, another account will take over. But only if you remove it from the campaign's list manually.
Q: What will happen with sending in my campaign if my email account is disconnected?
A: If an account is simply disconnected or removed from the email accounts dashboard, then the campaign waits for it. You need to remove it from the campaign itself for another account to take over.