ServerPilot installs and configures Postfix so your scripts can send email from your server. However, ServerPilot does not manage mail servers for hosting your domain's email.
If you need to receive email at your domain, you can either use a mail forwarding service, a mail hosting service, or run your own mail servers.
If you only need email sent to your domain to be forwarded to another email address, you don't need full email hosting but instead just an email forwarding service.
Mail forwarding allows you to have mail that is sent to name@YOUR_DOMAIN automatically forwarded to another address, such as an @gmail.com address. You can then configure your Gmail account to send mail from your domain's email address so people see emails you send from Gmail as coming from name@YOUR_DOMAIN.
There are free email forwarding services, but they sometimes have restrictions. Namecheap offers a free email forwarding service, but it requires you to use Namecheap's nameservers for your domain's DNS.
Paid forwarding services are inexpensive and generally don't have the same restrictions. Hover offers mail forwarding for $5/year (that is, $5 for an entire year) for each forwarded address.
Another option for email forwarding is to use Mailgun. Mailgun allows you to forward up to 50,000 emails per month for $35/month. To use Mailgun to forward mail, you would sign up for a Mailgun account, add your domain and follow their steps to verify domain ownership, and then create "Routes" to forward your incoming mail.
A third-party mail hosting provider handles all aspects of your domain's email. You point your domain's MX records to their mail servers so mail sent to your domain goes directly to their servers. They provide spam filtering and webmail. They also provide POP and IMAP access to your mail as well as SMTP servers that can be configured with local email clients like Outlook.
Wikipedia has a good comparison of webmail providers.
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Using Google Apps for your domain, every account at your domain will have access to the same Gmail webmail interface your users are used to with their @gmail.com accounts. However, all email sent and received will be for your domain name, not for @gmail.com.
You can also use Google Groups as mailing lists for your domain.
Features: See Google Apps email features.
Pricing: Starts at $6/user/month when billed annually. See Google Apps pricing.
Pricing: Starts at $6/user/month when billed annually. See Office 365 pricing.
Pricing: Starts at $1/user/month. See Zoho pricing.
Pricing: Starts at $3/user/month. See FastMail pricing.
If you want to host your own mail, you can run a separate server (not managed by ServerPilot) and either install the entire mail hosting stack yourself or use one of the following control panels to manage mail.
iRedMail is a control panel focused entirely on email hosting. As a result, if you only need to use a server for mail management, using iRedMail won't have the bloat or complexity of cPanel or Plesk.
Pricing: Free (open source)
Features: See iRedMail features.
cPanel can be used to only manage email. If you are hosting your websites on servers using ServerPilot, you'd only point your MX servers to your cPanel server that is hosting mail.
Pricing: Starts at $15.99/server/month. See cPanel pricing.
Plesk can be used to only manage email. If you are hosting your websites on servers using ServerPilot, you'd only point your MX servers to your Plesk server that is hosting mail.
Features: There is no Plesk page focusing on email features.
Pricing: Starts at $12.38/server/month. See Plesk pricing.