But I was facing some issues with the delivery rate.

I sent a broadcast to 2034 contacts, but the initial delivery rate is only 17.60% (358). Then I clicked the resend to those who didn't open it.

I have tried to resend 3 times, but some of the emails still couldn't reach me. But my credits have been deducted 3 times. (Sometime the broadcast able to reach me sometime it failed)

It's considered a very low delivery rate for agencies. Is there any way to avoid this issue?