I have a DNN version 4.0.2 install which is using the built in Newsletter module to send a monthly newsletter out to just under 300 registered users.  The problem seems to be a large number of people are not recieving the email newsletter.

When I send the newsletter I use the Registered User option to send it to and it acts like it sends it because it does not give an error and I get the message that the newsletter was sent.  Some of us get it but most don't so since some of us get it I know the email account used by DNN is configured correctly or none of us would get it.  I've noticed that the typical Bulk Email Confirmation message which typically goes to the admin email account does not get sent after the newsletter is sent so there is no indication to the number of email messages sent.  I do get the Bulk Email Confirmation message to the admin email account when I am doing my testing of the newsletter when I send it to myself to verify how it looks before sending it out to everyone. 

When I look at the DNN Log Viewer I do not see any error messages or anything there to indicate any issues when the newsletter is sent out.

I have looked at all the settings and options that I know to look at and see nothing wrong.  Are there other places to look?

Does the newsletter module with this version of DNN handle this many email newsletters being sent out or is there some sort of limit to it that I do not know about or are there issues with the module itself that prevent it from working on sites of this size?

Another culprit could be your host.  I was having that issue only to find out my host has a limit to the number of emails that are sent out per minute, per day, etc.  So although DNN "sent" all the emails...the host picked and chose which to actually send and many didn't get the emails.

It would be nice to have a DNN specific setting to queue and throttle emails sent out from the portal based on settings to prevent this but it's not in my DNN3.2.2 version that I know of.  Not sure about the newer versions.

I have given this some thought as well and am thinking of trying something different when I send out the next newsletter by insteading of trying to send to say all registered users use the email box and input a set number of email addresses and send the newsletter multiple times to small groups and see if that has any effect.

The newer versions of DNN do not have the types of configuration settings that you mentioned in order to throttle the rate at which the emails are sent out, so there is always the potential to run into issues of larger distributions hitting hosting provider limits.

Thanks for the thoughts though, it is always good to exchange ideas on what the possibilities might be.