Integrating Proofpoint and Mimecast Email Security with Microsoft Sentinel

Microsoft Sentinel can ingest rich email security telemetry from Proofpoint and Mimecast to power advanced phishing detection. The Proofpoint On Demand (POD) Email Security and Proofpoint Targeted Attack Protection (TAP) connectors pull threat logs (quarantines, spam, phishing attempts) and user click data into Sentinel. Similarly, the Mimecast Secure Email Gateway connector ingests detailed mail flow and targeted-threat logs (attachment/URL scans, impersonation events). These integrations use Azure-hosted ingestion (via Logic Apps or Azure Functions) and the new Codeless Connector framework to call vendor APIs on a schedule. The result is a consolidated dataset in Sentinel’s Log Analytics, enabling correlated alerting and hunting across email, identity, and endpoint signals. 

Figure: Phishing emails are processed by Mimecast’s gateway and Proofpoint POD/TAP services. Security logs (delivery/quarantine events, malicious attachments/links, user clicks) flow into Microsoft Sentinel. In Sentinel, these mail signals are correlated with identity (Azure AD), endpoint (Defender) and network telemetry for end-to-end phishing detection.

Proofpoint POD (Email Protection) Connector

The Proofpoint POD connector ingests core email protection logs. It creates two tables, ProofpointPODMailLog_CL and ProofpointPODMessage_CL. These logs include per-message metadata (senders, recipients, subject, message size, timestamps), threat scores (spamScore, phishScore, malwareScore, impostorScore), and attachment details (number of attachments, names, hash values and sandbox verdicts). Quarantine actions are recorded (quarantine folder/rule) and malicious indicators (URL or file hash) and campaign IDs are tagged in the threatsInfoMap field. For example, each ProofpointPODMessage_CL record may carry a sender_s (sender email domain hashed), recipient list, subject, and any detected threat type (Phish/Malware/Spam/Impostor) with associated threat hash or URL.

Deployment: Proofpoint POD uses Sentinel’s codeless connector (an Azure Function behind the scenes). You must provide Proofpoint API credentials (Cluster ID and API token) in the connector UI. The connector periodically calls the Proofpoint SIEM API to fetch new log events (typically in 1–2 hour batches). The data lands in the above tables. (Older custom logic-app approaches similarly parse JSON output from the /v2/siem/messages endpoints.)

Proofpoint TAP (Targeted Attack Protection) Connector

Proofpoint TAP provides user-click and message-delivery events. Its connector creates four tables: ProofPointTAPMessagesDeliveredV2_CL, ProofPointTAPMessagesBlockedV2_CL, ProofPointTAPClicksPermittedV2_CL, and ProofPointTAPClicksBlockedV2_CL. The message tables report emails with detected threats (URL or attachment defense) that were delivered or blocked by TAP. They include the same fields as POD (message GUID, sender, recipients, subject, threat campaign ID, scores, attachments info). The click tables log when users click on URLs: each record has the URL, click timestamp (clickTime), the user’s IP (clickIP), user-agent, the message GUID, and the threat ID/category. These fields allow you to see who clicked which malicious link and when. As the connector description notes, these logs give “visibility into Message and Click events in Microsoft Sentinel” for hunting.

Deployment: The TAP connector also uses the codeless framework. You supply a TAP API service principal and secret (proofpoint SIEM API credentials) in the Sentinel content connector. The function app calls TAP’s /v2/siem/clicks/blocked, /permitted, /messages/blocked, and /delivered endpoints. The Proofpoint SIEM API limits queries to 1-hour windows and 7-day history, with no paging (all events in the interval are returned). (A Logic App approach could also be used, as shown in the Tech Community blog: one HTTP GET per event type and a JSON Parse before sending to Log Analytics.)

Mimecast Secure Email Gateway Connector

The Mimecast connector ingests the Secure Email Gateway (SEG) logs and targeted-threat (TTP) logs. Inbound, outbound and internal mail events from the Mimecast MTA (receipt, processing, delivery stages) are pulled via the API. Typical fields include the unique message ID (aCode), sender, recipient, subject, attachment count/names, and the policy actions or holds (e.g. spam quarantine). For example, the Mimecast “Process” log shows AttCnt, AttNames, and if the message was held (Hld) for review. Delivery logs include the success/failure and TLS details. In addition, Mimecast TTP logs are collected: URL Protect logs (when a user clicks a blocked URL) include the clicked URL (url), category (urlCategory), sender/recipient, and block reason. Impersonation Protect logs capture spoofing detections (e.g. if an internal name is impersonated), with fields like Sender, Recipient, Definition and Action (hold/quarantine). Attachment Protect logs record malicious file detections (filename, hash, threat type).

Deployment: Like Proofpoint, Mimecast’s connector uses Azure Functions via the Sentinel content hub. You install the Mimecast solution, open the connector page, then enter Azure app credentials and Mimecast API keys (API Application ID/Key and Access/Secret for the service account). As shown in the deployment guide, you must provide the Azure Subscription, Resource Group, Log Analytics Workspace and the Azure Client (App) ID, Tenant ID and Object ID of the admin performing the setup. On the Mimecast side, you supply the API Base URL (regional), App ID/Secret and user Access/Secret. The connector creates a Function App that polls Mimecast’s SIEM APIs on a cron schedule (default every 30 minutes). You can optionally specify a start date for backfilling up to 7 days of logs. The default tables are MimecastSIEM_CL (for email flow logs) and MimecastDLP_CL (for DLP/TTP events), though custom names can be set.

Ingestion Considerations

• Data Latency: All these connectors are pull-based and typically run on a schedule (often 30–60 minutes). For example, the Proofpoint POD docs note hourly log increments, and Mimecast logs are aggregated every 30 minutes. Expect a delay of up to an hour or more from event occurrence to Sentinel ingestion.
• Schema Nuances: The APIs often return nested arrays and optional fields. For instance, the Proofpoint blog warns that some JSON fields can be null or vary in type, so the parse schema should account for all possibilities. Similarly, Mimecast logs come in pipe-delimited or JSON format, with values sometimes empty (e.g. no attachments). In KQL, use tostring() or parse_json() on the raw _CL columns, and mv-expand on any multivalue fields (like message parts or threat lists).
• Table Names: Use the connector’s tables as listed. For Proofpoint: ProofpointPODMailLog_CL and ProofpointPODMessage_CL; for TAP: ProofPointTAPMessagesDeliveredV2_CL, ProofPointTAPMessagesBlockedV2_CL, ProofPointTAPClicksPermittedV2_CL, ProofPointTAPClicksBlockedV2_CL. For Mimecast SEG/TTP: MimecastSIEM_CL (seg logs) and MimecastDLP_CL (TTP logs).
• API Behavior: The Proofpoint TAP API has no paging. Be aware of timezones (Proofpoint uses UTC) and use the Sentinal ingestion TimeGenerated or event timestamp fields for binning.

Detection Engineering and Correlation

To detect phishing effectively, we correlate these email logs with identity, endpoint and intel data:

• Identity (Azure AD): Mail logs contain recipient addresses and (hashed) sender user parts. A common tactic is to correlate SMTP recipients or sender domains with Azure AD user records. For example, join TAP clicks by recipient to the user’s UPN. The Proofpoint logs also include the clicker’s IP (clickIP); we can match that to Azure AD sign-in logs or VPN logs to find which device/location clicked a malicious link. Likewise, anomalous Azure AD sign-ins (impossible travel, MFA failure) after a suspicious email can strengthen the case.
• Endpoints (Defender): Once a user clicks a bad link or opens a malicious attachment (captured in TAP or Mimecast logs), watch for follow-on behaviors. For instance, use Sentinel’s DeviceSecurityEvents or DeviceProcessEvents to see if that user’s machine launched unusual processes. The threatID or URL hash from email events can be looked up in Defender’s file data. Correlate by username (if available) or IP: if the email log shows a link click from IP X, see if any endpoint alerts or logon events occurred from X around the same time. As the Mimecast integration touts, this enables “correlation across Mimecast events, cloud, endpoint, and network data”.
• Threat Intelligence: Use Sentinel’s ThreatIntelligenceIndicator tables or Microsoft’s TI feeds to tag known bad URLs/domains in the email logs. For example, join ProofPointTAPClicksBlockedV2_CL on the clicked url against ThreatIntelligenceIndicator (type=URL) to automatically flag hits. Proofpoint’s logs already classify threats (malware/phish) and provide a threatID; one can enrich that with external intel (e.g. check if the hash appears in TI feeds). Mimecast’s URL logs include a urlCategory field, which can be mapped to known malicious categories. Automated playbooks can also pull Intel: e.g. use Sentinel’s TI REST API or Azure Sentinel watchlists containing phishing domains to annotate events.

In summary, a robust detection strategy might look like: (1) Identify malicious email events (high phish scores, quarantines, URL clicks). (2) Correlate these events by user with Azure AD logs (did the user log in from a new IP after a phish click?). (3) Correlate with endpoint alerts (Defender found malware on that device). (4) Augment with threat intelligence lookups on URLs and attachments from the email logs. By linking the Proofpoint/Mimecast signals to identity and endpoint events, one can detect the full attack chain from email compromise to endpoint breach.

KQL Query

Here are representative Kusto queries for common phishing scenarios (adapt table/field names as needed):

• Malicious URL Click Detection: Identify users who clicked known-malicious URLs.

For example, join TAP click logs to TI indicators:This flags any permitted click where the URL matches a known threat indicator. Alternatively, aggregate by domain:

let TI = ThreatIntelligenceIndicator

| where Active == true and _EntityType == "URL";

ProofPointTAPClicksPermittedV2_CL

| where url_s != ""

| project ClickTime=TimeGenerated, Recipient=recipient_s, URL=url_s, SenderIP=senderIP_s

| join kind=inner TI on $left.URL == TI._Value

| project ClickTime, Recipient, URL, Description=TI.Description

This flags any permitted click where the URL matches a known threat indicator. Alternatively, aggregate by domain:

ProofPointTAPClicksPermittedV2_CL 

| extend clickedDomain = extract(@"https?://([^/]+)", 1, url_s)

| summarize ClickCount=count() by clickedDomain

| where clickedDomain has "maliciousdomain.com" or clickedDomain has "phish.example.com"

• Quarantine Spike (Burst) Detection: Detect sudden spikes in quarantined messages.

For example, using POD mail log:This finds hours with an unusually high number of held (quarantined) emails, which may indicate a phishing campaign. You could similarly use ProofPointTAPMessagesBlockedV2_CL.

ProofpointPODMailLog_CL

| where action_s == "Held"

| summarize HeldCount=count() by bin(TimeGenerated, 1h)

| order by TimeGenerated desc | where HeldCount > 100

• Targeted User Phishing: Find if a specific user received multiple malicious emails. E.g., for user email address removed for privacy reasons:This lists recent phish attempts targeting Username. You might also join with TAP click logs to see if she clicked anything.

ProofpointPODMessage_CL |

where recipient has "email address removed for privacy reasons"

| where array_length(threatsInfoMap) > 0 and threatsInfoMap_classification_s == "Phish"

| project TimeGenerated, sender_s, subject_s, threat=threatsInfoMap_threat_s

• Campaign-Level Analysis: Group emails by Proofpoint campaign ID to see scope of each campaign:This shows each campaign ID with how many unique recipients were hit and one example subject. Combining TAP and POD tables on GUID_s or QID_s can further link click events back to the originating message/campaign.

ProofpointPODMessage_CL

| mv-expand threatsInfoMap

| summarize Recipients=make_set(recipient), Count=dcount(recipient) by CampaignID=threatsInfoMap_campaignId_s

| project CampaignID, RecipientCount=Count, Recipients, SampleSubject=any(subject_s)

Each query can be refined (for instance, filtering only within a recent time window) and embedded in Sentinel Analytics rules or hunting. The key is using the connectors’ fields – URLs, sender/recipient addresses, campaign IDs – to pivot between email data and other security signals.