sending out html newletter

I send out a newsletter monthly to only subscribed users.
I have been sending straight from outlook but I am wondering if there is any software on the web that could make this more efficent. It seems not everyone is getting the newsletters.

What can you advise?

Tell them to check their Junk/Spam/Bulk Mail folder.

I expect there are utilities for that written in PHP or ASP.

There are a lot of possible issues. A couple years ago I wrote a mass emailing program and it was quite an education. The mail server we were using was behind a firewall and not using a "real" domain name, that only made many of the recipients mail servers bounce us. Our ISP would shut us down from time to time for sending out too much volume and this was a business account. I could go on and on, but the only way to solve your problem is to test and troubleshoot until you get it worked out. When someone doesn't get the mail find out as much as you can about their setup and try to replicate it.

I don't know about commercial products but I wrote the one we used in about 2 weeks and it included the ability to queue up an unlimited number of campaigns, schedule their kickoff, throttle mail output to keep us from looking like a spammer (it would trickle them out overnight if it had to), and reports to show not only how many had been viewed, but how many click throughs there were to the campaign websites. Any decent programmer should be able to whip up something similar.

i would suggest checking out phpMailer Class, it works well for sending mass html emails out.