We have a PHP app running along side our original classic .asp application on a WIndows 2012 R2 server running IIS. In our original app we used MailEnable (free version) to allow us to send emails out. However this solution is no longer working for us.
Here is a brief summary of what happens... the users have their own email addresses - which they prefer to send FROM - and they want to send updates and invoices to their clients. Ten years ago sending "From" their own email addresses was not much of a problem. Now with the spam filters and other issues, many of these emails fail to send.
Also many of our users are still maintaining their original public email addresses - lots of Yahoo, AOL, etc. email addresses. This too, is becoming an issue.
As we have tried sending FROM their email address TO their clients, deliverability has dropped significantly. The sending IP doesn't match the FROM domain IP and won't deliver - even though it's not spam or any deceitful type of email. These are legitimate emails needing delivered from our users to their clients.
So what I am asking for is suggestions as to HOW to get emails delivered to the clients, and still keep our users happy. We did setup a specific email address to be sent FROM so the sending email matches the sending IP, as well as also setting the REPLY TO address back to the user's email itself. However, the users panic when their clients ask if they have a new email address (our standard email used by all sends). They don't want their clients sending to that email address and then not receive their emails. We too, would have no idea which client belonged to which user.
We have thought about using a third-party SMTP service for deliverability, but then again they do not allow for the use of public email addresses either.
Suggestions anyone? Of course keeping it as low-cost as possible. Currently we are stuck between a rock and a hard place converting our classic app to the new PHP format. So money is tight, but we definitely need a solution ASAP.