We use nxlog for this, with the followin configuration snippet:

<Extension w3c>
    Module xm_csv
    Fields $date, $time, $s_ip, $cs_method, $cs_uri_stem, $cs_uri_query, $s_port, $cs_username, $c_ip, $cs_User_Agent, $cs_Referer, $sc_status, $sc_substatus, $sc_win32_status, $time_taken
    FieldTypes string, string, string, string, string, string, integer, string, string, string, string, integer, integer, integer, integer
    Delimiter ' '
</Extension>

<Input messagetracking_in>
    Module 	 im_file
    File 	 '<PATH TO EXCHANGE LOGS>\MessageTracking\MSGTRK*.LOG'
    PollInterval 1
    Recursive True
    SavePos True
    ReadFromLast True
    Exec 	 $FileName = file_name();
    Exec 	 if ($raw_event == '') drop();
    Exec 	 if ($raw_event == ';') drop();
    Exec 	 $ModuleType = 'file_collection';
</Input>

<Input iis_in>  
    Module    im_file
    File      '<PATH TO IIS LOGS>\inetpub\W3SVC1\u_ex*'
    ReadFromLast True
    Recursive True
    PollInterval 1
    SavePos True
    # drop first line, which is CSV header line
    Exec if $raw_event =~ /^#/ drop();                      \
       else                                                 \
       {                                                    \
            w3c->parse_csv();                               \
            $EventTime = parsedate($date + " " + $time);    \
            $SourceName = "IIS";                            \
            $raw_event = to_json();                         \
       }
</Input>

Equally, you should be able to just use the Logpoint Agent (and in the future AgentX) and set up a file collection for those locations, i.e. the Message Tracking log, the SMTP log and the IIS log for OWA. There is both a specific normaliser for Exchange IIS as well as the generic IIS compiled normaliser, there is a normaliser for on-premise Exchange Message Tracking logs, and there is a normaliser for the Exchange SMTP logs as well.

Just for completeness, unfortunately there isn’t an easy way of collecting on-premise Exchange Audit logs, i.e. who made changes to mailboxes, permissions etc. That’s trivial in Office 365, but on-premise it relies on either a custom script, a paid for module for NXlog, or another third party utility like LogBinder.