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General settings

With general settings, you can turn Sophos Firewall into a mail transfer agent (MTA) or a transparent mail proxy.

SMTP deployment mode

To switch between MTA and legacy modes, click the button.

In legacy mode (transparent mail proxy), you can specify policies to protect emails from spam, malware, and data leakage. You can also specify encryption settings.

In MTA mode, Sophos Firewall routes and protects emails of protected domains on more than one mail server. You can specify inbound and outbound mail relay, and configure encryption and quarantine settings. You can also view the cause of delay in email delivery and view mail logs.

Note

If you've migrated from CyberoamOS or SFOS v15 to SFOS v16, legacy mode is automatically enabled.

Outbound banner settings

Email banner mode: The method of adding a banner to outgoing emails.

Note

To add a banner, you must select SMTP and SMTPS scanning in firewall rules.

Email banner: Text added to outgoing emails.

Note

You can only add text banners.

Example

This email contains confidential information. You are not authorized to copy the contents without the sender's consent. Print this email only if it's necessary. Spread environmental awareness.

SMTP settings

SMTP hostname: SMTP hostname used in HELO and SMTP banner strings. Default hostname: Sophos.

Note

Applicable only to system-generated notification emails.

Don't scan emails greater than: Maximum file size (KB) for scanning. Files received over SMTP/S that exceed this size won't be scanned. 0 sets the file size limit to 51,200 KB.

Action for oversize emails: Action for emails that exceed the specified size.

Name Description
Accept Forwards to the recipient without scanning.
Reject Rejects the email and notifies the sender.
Drop Drops the email without notifying the sender.

Bypass spam check for SMTP/S authenticated connections: Bypasses spam check for emails received over SMTP/S connections that are authenticated by the mail server.

Verify sender's IP reputation: Verifies reputation of sender’s IP address. Specify action for spam and probable spam.

Note

Sophos Firewall checks the sender's IP reputation before the spam checks specified in the SMTP policy.

Name Description
Accept Scans and forwards to recipient
Reject Rejects the email and notifies the sender.
Drop Drops the email without notifying the sender.

SMTP DoS settings: Protect the network from SMTP denial-of-service attacks.

Settings Description Acceptable range
Maximum connections Connections that can be established with mail server. 1 to 20000
Maximum connections/host Connections allowed from a host to mail server. 1 to 10000
Maximum emails/connection Emails that can be sent over a connection. 1 to 1000
Maximum recipients/email Recipients of a single email. 1 to 256
Emails rate Emails from a host in a minute. 1 to 20000
Connections rate Connections from a host to the mail server in a second. 1 to 20000

POP/S and IMAP/S settings

Don't scan emails greater than: Maximum email size (in KB) for scanning. Emails received over POP/IMAP that exceed this size won't be scanned. 0 sets the size limit to 10,240 KB.

Recipient headers: Header values scanned to detect the recipients specified in POP/IMAP policies. Default: Delivered-To, Received, X-RCPT-TO

Ports

Sophos Firewall uses the following standard ports for emails:

  • SMTP: Port 25
  • SMTPS: Port 465
  • POP3: Connection upgraded to SSL/TLS using STARTTLS extension on port 110
  • POP3S: SSL/TLS over POP3 on port 995
  • IMAP: Connection upgraded to SSL/TLS using STARTTLS extension on port 143
  • IMAPS: SSL/TLS over POP3 on port 993

STARTTLS upgrades unsecured POP3/IMAP connections to SSL/TLS sessions on the same port.

Note

You can also configure email scanning for ports other than the standard ports 25, 587, and 465.

SMTP TLS configuration

Specify the settings to secure SMTP traffic.

TLS certificate: CA certificate or server certificate to scan SMTP traffic over SSL.

Allow invalid certificate: Select to allow SMTP traffic over SSL connections with an invalid certificate from the mail server. To reject such connections, clear the check-box.

Disable legacy TLS protocols: Select to turn off protocols earlier than TLS 1.1.

Note

To overcome TLS vulnerabilities, we recommend that you turn off legacy TLS protocols.

Require TLS negotiation: Select remote hosts (mail servers) or networks to enforce TLS encryption on their connections. Sophos Firewall will initiate TLS-secured connections for emails sent to the selected hosts or networks. You can specify up to 512 host entries.

Note

If TLS is enforced but a connection can't be established, Sophos Firewall discards emails to the specified remote host or network.

Require sender email domains: Specify the sender domain to enforce TLS encryption on email connections. You can specify up to 512 host entries.

Note

If TLS is enforced but a connection can't be established, Sophos Firewall discards emails from these sender domains.

Skip TLS negotiation: Select the remote hosts (mail servers) or networks to skip TLS encryption on their connections. Sophos Firewall establishes unencrypted SMTP connections to these hosts. You can specify up to 512 host entries.

POP and IMAP TLS configuration

Specify the settings to secure POP/IMAP traffic.

TLS certificate: CA certificate to scan POP and IMAP traffic over SSL.

Allow invalid certificate: Select to allow POP and IMAP traffic over SSL connections with an invalid certificate from the mail server. To reject such connections, clear the check-box.

Disable legacy TLS protocols: Select to turn off protocols earlier than TLS 1.1.

Note

To overcome TLS vulnerabilities, we recommend that you turn off legacy TLS protocols.

Email journaling

You can store incoming emails of one or more recipients and forward these emails to administrators.

  • To add an email journal, click Add.

Spam check exceptions

Domain name: Enter the domains for which you want to skip spam checks.

Malware protection

Malware protection is available in Sophos Firewall XG 105, Cyberoam CR500iNG, Sophos UTM SG105, and later models.

Sophos Firewall offers scanning by two antivirus engines.

Primary antivirus engine

Select the primary antivirus engine to scan traffic from the following options:

  • Sophos
  • Avira. If you select this, Sophos Firewall will turn off Zero-day protection in SMTP policies with single antivirus scan.

Note

If you've selected dual antivirus in the SMTP policy, the primary engine scans traffic first, and then the secondary engine scans traffic. If you've selected single antivirus, only the primary engine scans traffic.

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