Adversaries may target user email to collect sensitive information from a target.
Files containing email data can be acquired from a user's system, such as Outlook storage or cache files .pst and .ost.
Adversaries may leverage a user's credentials and interact directly with the Exchange server to acquire information from within a network.
Some adversaries may acquire user credentials and access externally facing webmail applications, such as Outlook Web Access.
APT1 uses two utilities, GETMAIL and MAPIGET, to steal email. GETMAIL extracts emails from archived Outlook .pst files, and MAPIGET steals email still on Exchange servers that has not yet been archived.
Use of encryption provides an added layer of security to sensitive information sent over email. Encryption using public key cryptography requires the adversary to obtain the private certificate along with an encryption key to decrypt messages.
Use of two-factor authentication for public-facing webmail servers is also a recommended best practice to minimize the usefulness of user names and passwords to adversaries.
Identify unnecessary system utilities or potentially malicious software that may be used to collect email data files or access the corporate email server, and audit and/or block them by using whitelisting  tools, like AppLocker,   or Software Restriction Policies  where appropriate. 
There are likely a variety of ways an adversary could collect email from a target, each with a different mechanism for detection.
File access of local system email files for Exfiltration, unusual processes connecting to an email server within a network, or unusual access patterns or authentication attempts on a public-facing webmail server may all be indicators of malicious activity.
Monitor processes and command-line arguments for actions that could be taken to gather local email files. Remote access tools with built-in features may interact directly with the Windows API to gather information. Information may also be acquired through Windows system management tools such as Windows Management Instrumentation and PowerShell.
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