MS Exchange Server Problem to Be Solved

This is a tiny project for someone who’s VERY experienced with an MSExchange server. We're experiencing two problems when sending mass-mailings from our ATS (PCR Applicant Tracking System) through our server. 1.) The mailings are going through extremely slowly. I checked with all possible sources for this problem (the makers of my ATS, my internet provider, etc.) and as of right now, it seems that the issue is actually my MSExchange server. Maybe there's a setting in there that only allows a certain number of mails per minute or a 'ping' before another e-mail can be sent ...?!? 2.) When I send messages through our ATS, it sometimes gives me the following error message: "Instead Reported Unable to read data from the transport connection: EndReceive can only be called once for each asynchronous operation" I checked with the developers of my ATS and they told me that this is an issue with our e-mail provider (I just sent an e-mail to my internet provider but I’m wondering if that is indeed an issue with my Exchange server as well as they are only providing the internet connection and no e-mail service). If you know exactly where to look for on our Exchange server to solve these issues, please provide your quote … or, ‘just in case’ this doesn’t look like an Exchange issue, any feedback would be very much appreciated. Thanks in advance! :)