Hi, I'm using forge to deploy my projects for a while now and I love it. I used to work with DirectAdmin.
One of the benefits of a server with DirectAdmin was that it has an email server as well. Lately almost every client has an office365 of google Apps account, so email is not an issue. However, right now I'm working on a budget project and it needs to include an email server.
@stefr Unfortunately that’s the downside of moving away from shared hosting: you lose infrastructure such as email services like this. You’re going to have to opt for a third-party service instead. Most ISPs and hosting companies offer this as a separate service for a couple of bucks per email address per month.
Do yourself a favour and encourage the client to use Google Apps for Business. It's $5/month per user, gives loads of storage - probably more than you're going to want to manage for them - web access, mobile, endless clients, and best of all you don't have to worry about supporting it. They get the benefit of all the other Google Apps, too.
Peace of mind for you and the client, and chances of support headaches for you get very small.
Of course, there is the option of installing your own email server on your existing server, but providing support for Email related issues can be crippling for a small business or freelancer. Hand that problem off to someone else :)
you could use directadmin/virtualmin/usermin, is gpl (have a free version) and comes with smtp, httpd, database and all you need to sharing hosting. https://www.virtualmin.com/
I also had the same problem, moving from CPanel to Forge/DigitalOcean.
Some domains registrars also offers hosted emails in their service. Great option, as you don't have to manage servers in this case. There are also "email only" providers like Zoho Mail, Fastmail, Rackspace Email, ...