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To run your own mail server on FlashRDP, first ask support to open outgoing port 25 (it’s blocked by default), then set reverse DNS for your mail hostname, install a mail stack such as Mail-in-a-Box, and publish MX, SPF, DKIM and DMARC records. Without all of these, other providers will reject or junk your mail. Running a mail server takes some Linux experience and ongoing care. You need a FlashRDP Linux VPS and a domain name you control.

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Step 1: Request outgoing port 25

Outgoing port 25 is blocked by default on every FlashRDP server to protect our IP addresses from spam listings. Until it’s opened, your server can’t deliver mail directly to other mail servers.Open a ticket with a short business justification (what you send, to whom, and roughly how much). Sending spam is prohibited under the Acceptable Use Policy, and an IP that ends up on a blocklist such as Spamhaus breaks it.

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Step 2: Set the hostname and reverse DNS

  1. Pick a mail hostname, for example box.yourdomain.com (Mail-in-a-Box’s convention) or mail.yourdomain.com.
  2. Create an A record for that hostname pointing to your server’s IP.
  3. Set the server’s reverse DNS to the same hostname from the Network tab of your server in the Billing Portal. See Configure Reverse DNS. Most large mail providers check that forward and reverse DNS match.

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The core components

A mail server is several programs working together:
  • Postfix (SMTP): sends mail to other servers and receives mail for your domain.
  • Dovecot (IMAP/POP3): lets mail apps such as Apple Mail, Outlook or Thunderbird read your mailbox.
  • Spam and virus filtering: for example SpamAssassin or Rspamd, and ClamAV.
  • DKIM signing: for example OpenDKIM, so receivers can verify your mail wasn’t altered.

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The easier way: Mail-in-a-Box

Wiring those components together by hand takes hours. Mail-in-a-Box installs a complete mail server with webmail, contacts and calendar, and creates most DNS records for you. Its setup guide requires a fresh Ubuntu 22.04 server dedicated to mail; check the Mail-in-a-Box guide for the currently supported release before you deploy. Log in via SSH and run the official installer:
This pipes a script from Mail-in-a-Box’s own site into a root shell. To review it first, download it with curl -s https://mailinabox.email/setup.sh -o setup.sh, read it, then run sudo -E bash setup.sh.
The installer asks for your email address and hostname, then prints the admin panel URL. Alternatives include iRedMail and Mailcow.

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DNS records you need

If you skip these, your mail will land in spam folders or be rejected. Mail-in-a-Box can host DNS for you; otherwise add them at your DNS provider:
  • MX: tells other servers where to deliver mail for your domain.
  • SPF: a TXT record listing which servers may send mail for your domain.
  • DKIM: a TXT record with the public key that verifies your mail’s signature.
  • DMARC: a TXT record telling receivers what to do with mail that fails SPF or DKIM.
  • Reverse DNS (PTR): set in Step 2. Required by almost all major providers.

Configure Reverse DNS (rDNS)

Connect via SSH

Open a Support Ticket

Acceptable Use Policy

Last modified on October 11, 2026