How does the e-mail system work?

I have more than 10 posts and have e-mailed a number of ladies using the EI e-mail facility on the ladies profile pages. I have done this when trying to contact ladies that are not set up for PM.

I've never got an error msg and have no way of knowing if my e-mail was delivered, but I have never received a single response from any of these ladies.

On the other hand when I contact a lady through PM or their stand alone website I always get a response - not always the response I want but you can't have everything!

Anyone know what's going on?