Customized Email List Server/Remailer

Here's a brief description of the product…it's basically a glorified list server. I have approximately 40,000 email addresses who have opted into a system. I have created about 400 different email distribution lists where the 40,000 people exist on one or more of the 400 lists. The average size of a an email list is about 800 email addresses. I want my 2,000 employees to be able to send an email to one or more of these email lists. The key is I want them to send the emails from whatever email client they want (outlook, blackberry, crm tool). I do not want to force the employee to login to a web application and send templated emails or have to copy/paste in their message. I suspect that we may send out 20-30 emails a day to a distribution. What I envision is a list server where I can daily FTP the 400 updated email distribution lists. Each email lists would be an individual file (e.g., [login to view URL], [login to view URL]). Each text file would map to a specific list serve distribution list email address (list1 @ xyzdomain . com, list2 @ xyzdomain . com). If one of my employees sends an email to list1 @ xyzdomain . com, emails would be generated from the employee's email address in the from/reply fields and individual emails would be generated to each person in the list with their name in the to field. The messages could be text or html. The list server is merely remailing the original message to each individual. Recipients could reply and the message would go back to the sending employee's email address. Should the employee send an email to multiple lists in one email (e.g., list1 @ xyzdomain . com;list2 @ xyzdomain . com), the list server should be able to deduplicate addresses across multiple lists. The list server should be efficient enough to sort the deduplicated destinations by domain and open a single conversation to each destination domain SMTP server. I would like the list server to only accept email where the from address of the sending email is from my company domain so only my employees can use these lists. (I realize this can be spoofed but this is good enough security for this application.) Security options like list serv passwords or moderator approval is not an option due to the lack of technical skills of the employees sending these emails. I would also like an opt out link in the footer of the emails, where a recipient can click, and be opted out of future mailings. Any tracking information on who sent emails and how many people the emails went to would be nice, but not necessary. There is no need to track if the recipients opened the email. I am also looking for a hosting provider that would be friendly to this type of opt-out emailing traffic. I would also like the developer to take care where possible to maximize the emails being delivered and not flagged automatically as SPAM. I would like the flexibility to change the IP/server/domain sending the email in the event the domain or server get's blocked by large carrier/spam lists.