I've a CentOS with CPanel server working as a SMTP server, which currently uses 20 different hostnames and IP addresses to deliver email for an email newsletter service.
However, it's extremely slow in sending emails. It's sending like 10 emails per minute, which I check by running the "exim -bpc" command. What could be affecting this?
One thing I'm supposing, is that there are frozen messages in the queue, which are slowing down the sending until they're sent out, and are putting new messages on hold.
What are the most common reasons a message can get frozen?
Also, would it be more efficient to use 20 different small VPSs to send out email rather than use one large VPS with the 20 different hostnames and IPs in it?