# Configuring the ESA to Accept Email

> Markdown source of <https://docs.calebsargeant.com/networking/cisco/core-security/email-security-with-cisco-esa/2.-configuring-the-esa-to-accept-email/>.

## Configuring Interfaces to Send and Receive Email

![image1](_images/configuring-the-esa-to-accept-email-1.png)

![image2](_images/configuring-the-esa-to-accept-email-2.png)

## Listeners and Host Access Tables

### Listeners

Listeners listen on the specified SMTP port for SMTP traffic

- Public Listener
  - Receives emails that are from other organizations with your org as the recipient
  - Public listener will only accept emails if the recipient domain is explicitly defined
- Private Listener
  - Receives emails that are from your org with outside organizations as the recipient

![image3](_images/configuring-the-esa-to-accept-email-3.png)

![image4](_images/configuring-the-esa-to-accept-email-4.png)

- Cisco sees over 300 billion emails daily
- Determine the likely hood that a sender is malicious or legitimate
  - IP Address of mail server
  - Reverse DNS lookup
  - Determine network owner
  - Organization controlling mail servers should be using IP space

## SMTP Deep Dive

### SMTP 3-Digit Codes

- 2 - Success - received, accepted and understood by the server
- 3 - Redirection - more information is required
- 4 - Temporary failure failure should be easily resolved
- 5 - Permanent failure - failure is unlikely to be resolved

### SMTP Envelope

``` text
<< 220 email.carvedrock.com SMTP
>> HELO email.globomantics.com
<< 250 email.carvedrock.com
>> MAIL FROM <kinda@globomantics.com>
<< 250 sender kinda@globomantics.com> ok
>> RCPT TO: <angie@carvedrock.com>
<< 250 recipient <angie@carvedrock.com> ok
```

### SMTP Headers

``` text
>> DATA
<< 354 go ahead
>> From: kinda <kinda@globomantics.com>
>> To: angie<angie@carvedrock.com>
>> Subject: Hello?
>> Date tue, 8 October 2019 21:28:30 -0800
```

X-headers can be used to send additional information in an email, but they are not required

### SMTP Body

``` text
>> Pluralsight has some of the best training
>> kinda
<< 250 ok
>> QUIT
<< 221 email.carvedrock.com
```

## Mail Flow Policies

### Mail Flow Policy Behaviors

- Relay - Used to forward outbound emails from Globomantics
  - Relay is the only behavior that does not require an associated Recipient Access Table (RAT)
- Accept - Used to accept incoming email from senders
- Reject - SMTP connection is started, but 400 or 500 code is sent
- TCP Refuse - No SMTP connection, sender may continue to try again
- Continue - No definitive action, try to match another sender group

![image5](_images/configuring-the-esa-to-accept-email-5.png)

![image6](_images/configuring-the-esa-to-accept-email-6.png)

## Integrating the ESA with LDAP and Recipient Access Table Deep Dive

### Integrating ESA with LDAP

- ESA will block emails if the recipient doesn’t exist
- Once LDAP is configured, by default all recipients will be verified

![image7](_images/configuring-the-esa-to-accept-email-7.png)

![image8](_images/configuring-the-esa-to-accept-email-8.png)

Place the more specific condition at the top, so it is matched before a more generalized condition