In a typical scenario - AR System Server is installed orginaly to use 64-bit Java, and at the time it's only necessary to have Outgoing email coming from the environment.

However, later on it's determined that Incoming email should be utilized, and the protocol to use must be MAPI.

Legacy ID:KA407873

The problem here is that there's a known incompatibility for Java:
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When running in a 64-bit JVM, the Email Engine cannot support the MAPI protocol
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This is documented in the Compatibility Matrix for AR System Server 7.6.04 onwards.
So you must incorporate 32-bit Java into the environment, and reconfigure the Email Engine to use the 32-bit Java in order to avail of using the MAPI protocol.

Steps
1) MAPI uses 32-bit Java, so this needs to be installed on the AR System Server machine

2) Login to the AR System Server machine as the target profile user, create the 32-bit Mail profile (ensure Outlook is installed)

3) Create the new Mailbox to use MAPI, select the profile above to use

4) Login as Administrator, set Log On tab of Email Engine Service to login as the Profile user, then log out

5) Login to the AR System Server machine as profile user

6) Make a copy of the EmailStart.bat, modify EmailStart.bat to use 32-bit Java as the below example:

echo off
rem =====================================================
rem This batch file assumes that it is being run from the install directory
rem and that java is in the the PATH.
rem =====================================================
rem -s servername -u username -p application password

set LIBVER=81_build001
set JavaPath=C:\Program Files (x86)\Java\jre7\bin
set JAVA_OPTS="-Xms256m -Xmx1024m -Djava.net.preferIPv4Stack=true -Djava.net.preferIPv6Addresses=false"

"%JavaPath%\java" "%JAVA_OPTS%" -cp emaildaemon.jar;.;log4j-1.2.14.jar;arapi%LIBVER%.jar;arutil%LIBVER%.jar;
activation.jar;icu4j.jar;mail.jar;imap.jar;smtp.jar;pop3.jar;armapi%LIBVER%.jar com.bmc.arsys.emaildaemon.EmailDaemon %*

7) Ensure the System Path statement includes the path for the 32-bit version of java (to the bin directory). Otherwise, even if the JVM LIbrary path is correct in the Registry Key as specified in step 9 below, the Email Engine Service may not start. For example: 

C:\Program Files (x86)\Java\jre1.8.0_201\bin;

8) Test the Email Engine functionality by starting it via the EmailStart.bat file from the command line

9) Modify the Registry for the Email Engine service to use 32-bit Java as the below example:

10) Backup the 64-bit binaries aremaild.exe and emaild.exe as aremaild_64.exe and emaild_64.exe

11) Swap in the 32-bit armaild.exe and emaild.exe binaries (Binaries are available in the installer, need to extract it)
<\ARSuiteKitWindows9.1.02\Disk1\files\emailengine\componentEmailEngineWindows>

12) Start the Email Engine service

NOTE: To get the required 32-bit binaries, you can either extract them from the installer (using the same version and Service Pack level you already have) or raise a support issue and request them to be sent to you.
Again you'll need to provide the version and Service Pack level you have so that you are sent the correct binaries.