Email Campaign Sending Very Slow

Email Campaign Sending Very Slow

I'm fairly new to Zoho. I've just recently transferred all of my email lists to Zoho Campaigns and sent my first large email blast out this morning. The email went to 48K recipients. 5 hours later, it's at 11%. At this rate, the email will take 2 days to complete sending. Is this normal? Am I doing something wrong? I've sent smaller email out from Zoho (1K) and they've sent rather quickly, so I'm surprised at this slow rate. Please help!