Smartermail can be pricey, but Kerio (which we utilized for over 8 years) was also expensive and unreliable and the recent purchase of Kerio has thrown tech support for that product into the dumper. Since we focus a lot on enterprise email, and our internal policy is to never mix email and hosting - we chose Smartermail years ago. We have extensive experience with Smartermail, Kerio and Icewarp - but of the 3, Smartermail is the most well-rounded product.
With Smartermail, using the Enterprise with some excellent anti-spam options in the open source community, we achieve a very stable mail system that easily handles mutliple thousands of users a day and keeps spam at a minimum. Cost is a bit under $1K a year at our level (and we have been customers a very long time)
At product setup, the Interworx site and Smartermail domains are created, along with their respective site/mail domain administrative users.
Afterward, the end user can handle Applications (Softaculous); FTP Accounts, Email Accounts(tied to Smartermail instead of Interworx); Email Forwarders, Mailing Lists, MySQL Databases, Cron Jobs, Subdomains, Domain Redirects, Domain Aliases, Interworx Backups and Unban of IP addresses as well as a Login to Interworx Button
Most customers then give the webmail URL to their own end-users, but the site owners/managers can easily add email accounts, mailing lists, mail fowarders from WHMCS (one portal to rule them all…)
Screenshot 2 of Mail: https://www.screencast.com/t/Hld60dBTAS
The Smartermail mailboxes may be setup through WHMCS or via a login to Smartermail from WHMCS - but having it handled in WHMCS has saved our team over 400 ticket request in the past 7 months compared to previous 7 months. Smartermail v15 and v16 (the new one is fantastic) are both supported, though dev for our company will focus on Smartermail 16 and above moving foward.
It is fully integrated in WHMCS, a nearly year-long process for us. The end user simply creates their account(s) and POOF they manage Interworx and Smartermail via our portal… makes brand loyalty much easier to promote.
IF you did not want to utilize the Smartermail option, the base Interworx Extended (we utilized it for about a year before the customization) gives the same options - all using Interworx for Hosting and Email.
Some additional things, since an end user may have multiple sites and multiple domains per site, there is some logic in the custom Interworx_Extended with Smartermail to help manage that.