Contents

Introduction

Prerequisites

Requirements

What It Means

Review and Troubleshoot

Step 1 - Verify the Number of Messages that PendDelivery

Step 2 - Verify the Host Status of a Destination Domain

Step 3 - Test SMTP Connectivity

Troubleshoot with Additional Methods

Related Information

Introduction

This document describes how to troubleshoot emails that are held on an Email Security Appliance (ESA) and that pend delivery.

Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

- CLI access to your ESA

- For Cloud Email Security (CES) client users, see  Command Line (CLI) Access for more information.

- GUI access to your ESA

What It Means

When you troubleshoot email delivery issues, the mail logs show that the last state of a message shows queued for delivery. This means that the message has been processed by the ESA, but that for some reason the ESA is unable to complete delivery of the message to the next-hop MTA. This could be for a variety of reasons, but commonly because the ESA is unable to reach the destination host and/or the messages are throttled or rejected by the next-hop MTA.

Review and Troubleshoot

Here are the steps when you need to review the messages queued for delivery and examine the SMTP connectivity.

Step 1 - Verify the Number of Messages that Pend Delivery

From the CLI, you can utilize the  tophosts  command sorted by Active Recipients to review items that are in the delivery queue. Active Recipients signifies the number of messages held that wait.

esa.lab.local> tophosts active_rcpts

Status as of: Thu Aug 13 14:29:42 2020 EDT

Hosts marked with '*' were down as of the last delivery attempt.

Active Conn. Deliv. Soft Hard

# Recipient Host Recip. Out Recip. Bounced Bounced

1 the.encryption.queue  0 0 0 0

2 the.euq.queue 5 0 0 0 0

3 the.euq.release.queue 0 0 0 0 0

From the GUI, you can navigate to Monitor > Delivery Status.

Delivery Status - Active Recipients

Step 2 - Verify the Host Status of a Destination Domain

From the CLI, you can utilize the  hoststatus command combined with the domain in question to review the Host up/down state. See Monitor the Status of a Mail Host.for more information.

esa.lab.local> hoststatus mail.com

Host mail status for: 'mail.com'

Status as of: Thu Aug 13 14:37:17 2020 EDT

Host up/down: up

Counters:

Queue

Soft Bounced Events 0

Completion

Completed Recipients 336

Hard Bounced Recipients 0

DNS Hard Bounces 0

5XX Hard Bounces 0

Filter Hard Bounces 0

Expired Hard Bounces 0

Other Hard Bounces 0

Delivered Recipients 336

Deleted Recipients 0

Gauges:

Queue

Active Recipients 0

Unattempted Recipients 0

Attempted Recipients 0

Connections

Current Outbound Connections 0

Pending Outbound Connections 0

From the GUI, this can also be seen under Monitor > Delivery Status.

Delivery Status - Latest Host Status

Some examples of the Host up/down status and what it can mean (not all-inclusive):

Terms

- Up - Reachable and actively accepts messages.

- Down - Positively down (for example, connection refused or no route to host) or the SMTP conversation is timed out.

- Unknown -Unable to connect (for example, delivery routed through an incorrect interface or IP address of the interface is not properly NAT/routed through the firewall).

Step 3 - Test SMTP Connectivity

If the host is unreachable, you can first check for the DNS MX records with dig and then test connectivity with telnet.

esa.lab.local> dig mx xmail.com

;; QUESTION SECTION:

;xmail.com. IN MX

;; ANSWER SECTION:

xmail.com. 1784 IN MX 40 al4.xmail-smtp-in.l.google.com.

xmail.com. 1784 IN MX 30 al3.xmail-smtp-in.l.google.com.

xmail.com. 1784 IN MX 10 al1.xmail-smtp-in.l.google.com.

xmail.com. 1784 IN MX 5 xmail-smtp-in.l.google.com.

xmail.com. 1784 IN MX 20 al.xmail-smtp-in.l.google.com.

esa.lab.local> telnet al1.xmail-smtp-in.l.google.com 25

Trying 10.233.186.26...

Connected to .

Escape character is '^]'.

220 mx.mail.com ESMTP d21si4412123pll.407 - gsmtp

If the telnet returns Connected with a 220 banner then retry the delivery with the  delivernow all  command. You can also navigate from the GUI to Monitor > Delivery Status and click Retry All Delivery.

Retry All Delivery

If the connectivity tests return a rejection then additional examination can be required. You can review the mail logs and/or Message Tracking to see if reasons for possible rejections are shown.

Troubleshoot with Additional Methods

- SMTPPING can be used to send a test message. For more information, see How to Troubleshoot Delivery Issues on the ESA.

- Packet captures allow you to review the SMTP conversation, and to confirm if any errors are seen (for example, TLS). For more information, see ESA - Packet Captures and Network Investigation. CES customers need to contact Cisco TAC to get assistance to run any captures.

- Domain Debug Logs also show the entirety of the SMTP conversation and are extremely useful if needing to see how messages are delivered from the ESA. For more information, see ESA Domain Debug Logs Configuration Example.

Related Information

- Access the Command Line Interface (CLI) of Your Cloud Email Security (CES) Solution

- Cisco Email Security Appliance - End-User Guides

- ESA Domain Debug Logs Configuration Example

- ESA - Packet Captures and Network Investigation

- How to Troubleshoot Delivery Issues on the ESA

- Monitor the Status of a Mail Host

- Cisco Technical Support & Downloads