Email servers sending high volume traffic to hosts
Last updated 2 days ago on 2026-07-17
About
The following analytic identifies a significant increase in data transfers from your email server to client hosts. It leverages the Network_Traffic data model to monitor outbound traffic from email servers, using statistical analysis to detect anomalies based on average and standard deviation metrics. This activity is significant as it may indicate a malicious actor exfiltrating data via your email server. If confirmed malicious, this could lead to unauthorized data access and potential data breaches, compromising sensitive information and impacting organizational security.
- Platform
Splunk
- Tags
- Data Source: SplunkDomain: ApplicationRule Type: QueryOS: Any
- Severity
- medium
- Risk Score
- 47
- False Positives
- The false-positive rate will vary based on how you set the deviation_threshold and data_samples values. Our recommendation is to adjust these values based on your network traffic to and from your email servers.
- Source
- View on GitHub(external, opens in a new tab or window)
Definition
- Rule Language
- SPL
- Rule Type
- query
text code block:| tstats `security_content_summariesonly` sum(All_Traffic.bytes_out) as bytes_out FROM datamodel=Network_Traffic WHERE All_Traffic.src_category=email_server BY All_Traffic.dest_ip _time span=1d | `drop_dm_object_name("All_Traffic")` | eventstats avg(bytes_out) as avg_bytes_out stdev(bytes_out) as stdev_bytes_out | eventstats count as num_data_samples avg(eval(if(_time < relative_time(now(), "@d"), bytes_out, null))) as per_source_avg_bytes_out stdev(eval(if(_time < relative_time(now(), "@d"), bytes_out, null))) as per_source_stdev_bytes_out BY dest_ip | eval minimum_data_samples = 4, deviation_threshold = 3 | where num_data_samples >= minimum_data_samples AND bytes_out > (avg_bytes_out + (deviation_threshold * stdev_bytes_out)) AND bytes_out > (per_source_avg_bytes_out + (deviation_threshold * per_source_stdev_bytes_out)) AND _time >= relative_time(now(), "@d") | eval num_standard_deviations_away_from_server_average = round(abs(bytes_out - avg_bytes_out) / stdev_bytes_out, 2), num_standard_deviations_away_from_client_average = round(abs(bytes_out - per_source_avg_bytes_out) / per_source_stdev_bytes_out, 2) | table dest_ip, _time, bytes_out, avg_bytes_out, per_source_avg_bytes_out, num_standard_deviations_away_from_server_average, num_standard_deviations_away_from_client_average | `email_servers_sending_high_volume_traffic_to_hosts_filter`
View this rule on Splunk
This rule was sourced from the official Splunk public repository. View the original rule on GitHub(external, opens in a new tab or window).