Configuring security profiles

Go to Profile > Security to create transport layer security (TLS) profiles and encryption profiles.

This section includes:

Configuring TLS security profiles
Configuring encryption profiles

Configuring TLS security profiles

The TLS tab lets you create TLS profiles, which contain settings for TLS-secured connections.

TLS profiles, unlike other types of profiles, are applied through access control rules and message delivery rules, not policies. For more information, see Controlling SMTP access and delivery.

To view the list of TLS profiles, go to Profile > Security > TLS.

GUI item

Description

Clone

(button)

Click the row corresponding to the profile whose settings you want to duplicate when creating the new profile, then click Clone. A single-field dialog appears. Enter a name for the new profile. Click OK.

Profile Name

Displays the name of the profile.

TLS Level

Displays the security level of the TLS connection.

None: Disables TLS. Requests for a TLS connection will be ignored.
Preferred: This is the default behavior. Whether TLS is used depends on the other party of the session.
Secure: Requires a certificate-authenticated TLS connection. CA certificates must be installed on the FortiMail unit before they can be used for secure TLS connections. For information on installing CA certificates, see Managing certificate authority certificates.

Action On Failure

Indicates the action the FortiMail unit takes when a TLS connection cannot be established, either:

Temporarily Fail: Reply to the SMTP client with a code indicating temporary failure.
Fail: Reject the email and reply to the SMTP client with SMTP reply code 550.

Optionally, you can choose to select the IBE on TLS failure option when configuring an encryption profile. For more information, see Configuring encryption profiles.

(Green dot in column heading)

Indicates whether or not the entry is currently referred to by another item in the configuration. If another item is using this entry, a red dot appears in this column, and the entry cannot be deleted.

To configure a TLS profile

Go to Profile > Security > TLS.

A dialog appears.

Either click New to add a profile or double-click a profile to modify it.
For a new profile, enter the Profile name.
From TLS option, select the security level of the TLS profile.
Configure the following, as applicable:

The availability of the following options varies by your selection in TLS option.

GUI item

Description

Check TLS version

Enable to select a Minimum TLS version to apply for the TLS profile.

The connection will be refused if the Minimum TLS version is not met, regardless of whether TLS option is set to Preferred or Secure.

SSL 3.0
TLS 1.0
TLS 1.1
TLS 1.2
TLS 1.3

DANE

Assign a DNS-based Authentication of Named Entities (DANE) support level:

None
Opportunistic
Mandatory (only available when TLS option is set to Secure)

For more information, see RFC 7929.

MTA-STS

Assign an MTA Strict Transport Security (MTA-STS) domain checking level.

Note that the MTA-STS feature may only take effect when enabled under System > Mail Setting > Mail Server Settings, or via the CLI Console:

config system mailserver

set smtp-mtasts-status {check-all-domain | check-external-domain | disable}

end

For more information, see Configuring SMTP service

Action on failure

Select whether to fail or temporarily fail if a TLS connection with the parameters described in the TLS profile cannot be established.

Check encryption strength

Enable to require a minimum level of encryption strength. Also configure Minimum encryption strength.

This option appears only if TLS option is Secure.

Minimum encryption strength

Enter the bit size of the encryption key. Greater key size results in stronger encryption, but requires more processing resources.

Check CA issuer

Enable and enter a string on the CA issuer field. The FortiMail unit will compare the string in the CA issuer field with the field with that same name in the installed CA certificates.

The CA issuer string format must use no spaces, and must use slashes "/" to separate the certificate components. For example:

/CN=Fortinet/O=Fortinet Ltd.

This option appears only if TLS level is Secure.

CA issuer

Select the type of match required when the FortiMail unit compares the string in the CA Issuer field and the same field in the installed CA certificates. For more information on CA certificates, see Managing certificate authority certificates.

Check CA issuer must be enabled for CA issuer to have any effect.

This option appears only if TLS level is Secure.

Lookup CA

To populate the CA issuer field with text from a CA certificate’s CA Issuer, select the name of a CA certificate that you have uploaded to the FortiMail unit.

Check certificate subject

Enable and enter a string in the Certificate subject field. The FortiMail unit will compare the string in the Certificate subject field with the field with that same name in the installed CA certificates.

The certificate subject string format must use no spaces, and must use slashes "/" to separate the certificate components. For example:

/CN=Fortinet/O=Fortinet Ltd.

This option appears only if TLS level is Secure.

Certificate subject

Select the type of match required when the FortiMail unit compares the string in the Certificate subject and the same field in the installed CA certificates.

Check certificate subject must be enabled for Certificate subject to have any effect.

This option appears only if TLS level is Secure.

Configuring encryption profiles

The Encryption tab lets you create encryption profiles, which contain encryption settings for secure MIME (S/MIME), identity-based encryption (IBE), and fallback to IBE if TLS delivery fails.

The ability to fallback automatically to IBE if TLS encryption fails ensures that all email is sent encrypted, even in instances where encryption keywords are used.

Encryption profiles are applied through either message delivery rules or content action profiles used in content profiles which are included in policies. For more information, see Configuring delivery rules and Configuring content action profiles.

Before S/MIME encryption will work, you must also create at least one internal address certificate binding. For details, see Configuring certificate bindings.

For more information about using S/MIME encryption, see Using S/MIME encryption.

For more information about using IBE, see Configuring IBE encryption.

To view or configure encryption profiles

Go to Profile > Security > Encryption.

GUI item	Description
Clone (button)	Click the row corresponding to the profile whose settings you want to duplicate when creating the new profile, then click Clone. A single-field dialog appears. Enter a name for the new profile. Click OK.
Profile Name	Displays the name of the profile.
Protocol	Displays the protocol used for this profile, S/MIME, IBE, or IBE on TLS failure.
TLS profile	Select the TLS profile for FortiMail to use first before falling back to the IBE profile, when necessary.
Encryption algorithm	Displays the encryption algorithm that will be used to encrypt the email (AES 128, AES 192, AES 256, CAST5 128, or Triple DES).
Action	For S/MIME, the actions are Encrypt, Sign, or Encrypt and Sign. For IBE, the action will be Encrypt only.
Action on failure	Indicates the action the FortiMail unit takes when S/MIME or IBE cannot be used: Drop and send DSN: Send a delivery status notification (DSN) email to the sender’s email address, indicating that the email is permanently undeliverable. Send plain message: Deliver the email without encryption. Enforce TLS: If the message delivery rule has no TLS profile or the TLS level in its profile is Preferred, the FortiMail unit will enforce the TLS Secure level. If the TLS level in its profile is None, then the email will temp fail because it contradicts with Enforce TLS. For more information, see Configuring delivery rules and Configuring TLS security profiles.
Access method	Displays the action used by the mail recipients to retrieve IBE messages. Push: A notification and a secure mail is delivered to the recipient who needs to go to the FortiMail unit to open the message. The FortiMail unit does not store the message. Pull: A notification is delivered to the recipient who needs to go to the FortiMail unit to open the message. The FortiMail unit stores the message.
Maximum size (KB) for Push method	Displays the settings of the maximum message size (KB) of the secure mail delivered (or pushed) to the recipient. If the message exceeds the size limit, it will be delivered with the Pull method.
(Green dot in column heading)	Indicates whether or not the entry is currently referred to by another item in the configuration. If another item is using this entry, a red dot appears in this column, and the entry cannot be deleted.

Either click New to add a profile or double-click a profile to modify it.

A dialog appears.

For a new profile, enter the name of the profile in Profile name.
In Protocol, select S/MIME or IBE.

The availability of the following options varies by your selection in Protocol.

If you selected IBE as the protocol:

Select the Action method (Push or Pull) for the mail recipients.
For Push, specify the maximum message size (KB) for the Push method (messages exceeding the size limit will be delivered with the Pull method).

If you select S/MIME as the protocol, select an action: Encrypt, Sign, or Encrypt and Sign. To use S/MIME encryption, you must also configure certificate binding. For details, see Using S/MIME encryption and Configuring certificate bindings.

From Encryption algorithm, select the encryption algorithm that will be used to encrypt email (AES 128, AES 192, AES 256, CAST5 128, or Triple DES).

From Action on failure, select the action the FortiMail unit takes when encryption cannot be used.

Drop and send DSN: Send a delivery status notification (DSN) email to the sender’s email address, indicating that the email is permanently undeliverable.
Send plain message: Deliver the email without encryption.
Enforce TLS: If the TLS level in the TLS profile selected in the message delivery rule is Encrypt or Secure, the FortiMail unit will not do anything. If the message delivery rule has no TLS profile or the TLS level in its profile is None or Preferred, the FortiMail unit will enforce the Encrypt level.

Click Create or OK.

Using S/MIME encryption

S/MIME (Secure/Multipurpose Internet Mail Extensions) is a standard for public key encryption and signing of MIME data. The FortiMail unit supports S/MIME encryption.

You can encrypt email messages with S/MIME between two FortiMail units. For example, if you want to encrypt and send an email from FortiMail unit A to FortiMail unit B, you need to do the following:

On FortiMail unit A:

import the CA certificate. For details, see Managing certificates.
create a certificate binding for the outgoing email to obtain FortiMail unit B’s public key in the certificate to encrypt the email. For details, see Configuring certificate bindings.
create an S/MIME encryption profile. For details, see Configuring encryption profiles.
apply the S/MIME encryption profile in a policy to trigger the S/MIME encryption by either creating a message delivery rule to use the S/MIME encryption profile (see Configuring delivery rules), or creating a policy to include a content profile containing a content action profile with an S/MIME encryption profile (see Controlling email based on sender and recipient addresses, Controlling email based on IP addresses, Configuring content action profiles, and Configuring content profiles).

If the email to be encrypted is matched both by the message delivery rule and the policy, the email will be encrypted based on the content profile in the policy.

On FortiMail unit B:

import the CA certificate. For details, see Managing certificates.
create a certificate binding for the incoming email and import both FortiMail unit B’s private key and certificate to decrypt the email encrypted by FortiMail unit A using FortiMail unit B’s public key.