I just moved my website from shared GoDaddy to a new VPS. Once moved, I changed my newsletter settings to my vps host and everything is working, it's just very slow. I have a fairly large subscriber list of nearly 18,000 and it takes about 3 days to send a newsletter. Usually, when sending some blog updates and such, that's not a big deal, but sometimes I have something important and I'd like some faster sending but I don't want to pay the big money it takes for something like Mailchimp or whatever with a list the size of mine. Is there any way I can speed up this sending with doing some setting changes or tweaks to my VPS?