In most cases when you want to send an emails in a campaign from a particular email account, you would also receive emails to the same account.
However some customers use this differently. They wish to send emails from one email account and receive replies to a different email account.
Also Email service providers like SendGrid and Mailgun do not support incoming emails. So when you send an email to a prospect from SendGrid or Mailgun you need to specifically have an account to receive replies to.
For this reason at the time of creation of campaign, SmartReach.io specifically prompts you to select emails to Send emails from and to Receive Replies To.
Select a different email account from sending email account or add a new email account here.