# Source: https://docs.datadoghq.com/security/default_rules/d9b-0f7-0a9.md

---
title: Inbound SMTP access should be restricted
description: Datadog, the leading service for cloud-scale monitoring.
breadcrumbs: >-
  Docs > Datadog Security > OOTB Rules > Inbound SMTP access should be
  restricted
---

# Inbound SMTP access should be restricted
 
## Description{% #description %}

Reduce the probability of a breach by checking [EC2 security groups](https://docs.aws.amazon.com/vpc/latest/userguide/VPC_SecurityGroups.html) for inbound rules that allow unfettered access to TCP port 25 (used by Simple Mail Transfer Protocol (SMTP) for email transmission) and restrict access to IP addresses that require this port.

## Rationale{% #rationale %}

Malicious activity, such as spamming, hacking, Shellshock, and denial-of-service (DoS) attacks, can occur when permitting unfettered access to this port.

## Remediation{% #remediation %}

### From the console{% #from-the-console %}

Follow the [Security group rules](https://docs.aws.amazon.com/vpc/latest/userguide/VPC_SecurityGroups.html#SecurityGroupRules) docs to learn how to add a security group rule that will restrict access to a specific port.

### From the command line{% #from-the-command-line %}

1. Run `revoke-security-group-ingress` to [remove inbound rules](https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ec2/revoke-security-group-ingress.html) that allow unrestricted access to port 25.

In the `revoke-security-group-ingress.sh` file:

   ```bash
       aws ec2 revoke-security-group-ingress
           --group-name group-name
           --protocol tcp
           --port 25
           --cidr 192.0.2.0/24
       
```

1. Run `authorize-security-group-ingress` to [add new inbound rules](https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ec2/authorize-security-group-ingress.html) that restrict port 25 access.

In the `revoke-security-group-ingress.sh` file:

   ```bash
       aws ec2 authorize-security-group-ingress
           --group-name your-group-name
           --protocol tcp
           --port 25
           --cidr 192.0.2.0/24
       
```