Home / Industry

Encrypting Inbound and Outbound Email Connections with PowerMTA

Don't miss a thing – sign up for CircleID Weekly Wrap newsletter delivered to your inbox once a week.

Encryption is becoming increasingly necessary when transferring data across the internet, and email is no different. In PowerMTA 4.5 and later there are several methods to encrypt both inbound and outbound connections. Here we'll provide a quick overview of how they may be achieved. Keep in mind, this document only deals with encrypting the channel, not the content.

Outbound Opportunistic Encryption

To use outbound opportunistic encryption in PowerMTA, simply add the following to your configuration file:

<domain *>
    use-starttls yes
    require-starttls no
</domain>

With this, PowerMTA will check to see if the remote mail server supports encryption. If it does, an attempt will be made to create an encrypted channel over which to send mail. If the encryption fails, or if no encryption is offered, then the mail is sent using no encryption.

To verify if the mail was sent over an encrypted channel, it is necessary to add additional fields to the CSV accounting file. This can be done with the following configuration:

<acct-file logacct.csv>
    records d, b
    record-fields d *, dlvTlsProtocol, dlvTlsCipher
    record-fields b *, dlvTlsProtocol, dlvTlsCipher
</acct-file>

If encryption is used, the above configuration will record the protocol and cipher used to deliver the message over an encrypted channel.

Outbound Client Certificate

While the vast majority of outbound connections do not require a local certificate, there may be some B2B cases in which the remote mail server requires PowerMTA to use a given certificate for encrypting the channel between the two servers. This can be facilitated in PowerMTA with a setup similar to the following:

<domain super-secure-server.com>
    smtp-client-certificate /path/to/certificate.pem password
    use-starttls yes
    require-starttls yes
</domain>

In the above example, any messages sent to super-secure-server.com will sent over an encrypted channel using the certificate /path/to/certificate.pem (in most cases supplied by the administrator of the remote mail server). If the encryption fails, the messages will not be sent.

Inbound Encryption

Of course, outbound traffic is only half of the traffic on a PowerMTA server. It may be required to encrypt the traffic coming into a PowerMTA server as well. This can be done in PowerMTA on a per <source> basis. The setup would look similar to the following:

#
smtp-listener 1.2.3.4:465 tls=yes
smtp-server-tls-certificate /etc/pmta/smtp-cert.pem "YourPasswordHere" smtp-server-tls-ciphers "HIGH:MEDIUM:!ADH:@STRENGTH"

<source 0/0>    # matches all
    allow-starttls yes
    require-starttls-before-auth yes
    allow-unencrypted-plain-auth no
</source>
#

Creation of the certificate /etc/pmta/smtp-cert.pem follows standard OpenSSL practices, and if assistance is needed in getting the certificate created (please contact support@port25.com). An example of the contents of the certificate is as follows:

-----BEGIN CERTIFICATE-----
YOUR CERT HERE
-----END CERTIFICATE-----
-----BEGIN RSA PRIVATE KEY----- Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,EBA505536010547C

YOUR PRIVATE KEY HERE
-----END RSA PRIVATE KEY-----

With this configuration all traffic connecting to 1.2.3.4 on port 465 can attempt to use encryption for transmitting email into PowerMTA.

Inbound Certificate Chain Validation

PowerMTA 4.5 and later supports the ability to validate certificate chains.

Evaluate PowerMTA (Free Trial) — PowerMTA compliments your technology stack whether it's on premise or in the cloud. Increasingly, cloud based senders and enterprises are integrating PowerMTA with other front end applications for maximum delivery and granular controls. Learn More

Port25

About Port25 – Port25, A Message Systems Company, provides highly focused email delivery software that addresses the ever-expanding needs of client communications and digital messaging apps. Port25's flagship product, PowerMTA™, has a global footprint, with over 4,000 installations in more than 51 countries. Learn More

Related topics: Cybersecurity, Email

 
   

Related Blogs

Related News

Explore Topics

Dig Deeper

Afilias Mobile & Web Services

Mobile Internet

Sponsored by Afilias Mobile & Web Services
Verisign

Cybersecurity

Sponsored by Verisign
Afilias

DNS Security

Sponsored by Afilias

Promoted Posts

Now Is the Time for .eco

.eco launches globally at 16:00 UTC on April 25, 2017, when domains will be available on a first-come, first-serve basis. .eco is for businesses, non-profits and people committed to positive change for the planet. See list of registrars offering .eco more»

Industry Updates – Sponsored Posts

Verisign Named to the Online Trust Alliance's 2017 Audit and Honor Roll

Attacks Decrease by 23 Precent in 1st Quarter While Peak Attack Sizes Increase: DDoS Trends Report

Leading Internet Associations Strengthen Cooperation

Verisign Releases Q4 2016 DDoS Trends Report: 167% Increase in Average Peak Attack from 2015 to 2016

Verisign Q3 2016 DDoS Trends Report: User Datagram Protocol (UDP) Flood Attacks Continue to Dominate

2016 U.S. Election: An Internet Forecast

Government Guidance for Email Authentication Has Arrived in USA and UK

ValiMail Raises $12M for Its Email Authentication Service

Don't Gamble With Your DNS

Defending Against Layer 7 DDoS Attacks

Understanding the Risks of the Dark Web

New TLD? Make Sure It's Secure

Verisign Releases Q2 2016 DDoS Trends Report - Layer 7 DDoS Attacks a Growing Trend

How Savvy DDoS Attackers Are Using DNSSEC Against Us

Facilitating a Trusted Web Space for Financial Service Professionals

MarkMonitor Partners with CYREN to Deepen Visibility into Global Phishing Attacks

Verisign Named to the Online Trust Alliance's 2016 Honor Roll

Port25 Announces Release of PowerMTA V4.5r5

New Case Study: Jobtome.com Replaces 30 Postfix Servers with a Single PowerMTA

Verisign Q1 2016 DDoS Trends: Attack Activity Increases 111 Percent Year Over Year