Custom email or aweber/icontact.etc

[thePHP]

right now my developer has been coding some back end things for me to manage my users with email. Everything is great, he made auto responders that i can edit and things of that sort...

i have heard that i can get blacklisted by not using things like aweber rather than my custom on site email manager to users.... is this true..

I recently realized it is lacking in analytics like open rate, click through rate etc but im sure if he really needed to do it it wouldn't be a problem. Any pros on cons to both approaches?

He already did it, so now to switch to aweber, he would disregard everything he did and just link the site up to aweber.
I would really appreciate the feedback, thank you.

[thePHP]

right now this is how it is set up..
the site is something like a myspace or forum where there are users who sign up and can contact one another.

currently this is what the system is doing with email....

1)
user signs up, but must be approved by me first, once i approve them a custom email goes out automatically (which i can edit however needed)

2) when a users internally messages another user, it hits their message box with their user name (no email displayed) then the system will email the user that received the message with a email notification saying :

hey you have received a message on xyx dot com please log in to view.. this not displaying the message senders email address...(again i can edit all of thisthis)

also there are features where i can internally message all users and i can break them down by different categories or i can mass message them directly to their email...... that is where im scared of getting blacklisted, mass emailing all of them.

so right now im very happy and it does what i want, but will this get messed up if i switch over to something like aweber?