Everything I've seen/read online seems to say that this policy bank is for a local sender, not a local recipient. It's almost like amavis is confusing the sender with the recipient.

This is a known bug, and will be fixed in upcoming iRedMail-0.9.3.
Here's the tutorial to fix it:
http://www.iredmail.org/docs/upgrade.ir … ernal-user
Note: This upgrade tutorial for iRedMail-0.9.3 is still a draft, do not apply other steps mentioned in above page.

Okay, I made the change.  I then did three emails:

1. one using the local mail client, mailing to a recipient in my domain.
2. one to an outside recipient.
3. one from my outside (work) email to my home email.

All 3 show as 'Passed CLEAN {RelayedInbound}'.  I suspect #1 and #2 are because the 'mail' command ends up using port 25 and not port 587?  Seems less than optimal.  Also, removal of the MYUSERS policy bank makes it impossible (?) to disable spam/antivirus for local users sending email?

Mail from root on iredmail to a local address:

Nov 18 09:45:35 iredmail postfix/qmgr[4173]: 7B8572C06D6: from=<root@druber.com>, size=865, nrcpt=1 (queue active)
Nov 18 09:45:35 iredmail postfix/smtpd[12977]: disconnect from iredmail.druber.com[127.0.0.1]
Nov 18 09:45:35 iredmail amavis[11734]: (11734-04) Passed CLEAN {RelayedInbound}, <root@druber.com> -> <dswartz@druber.com>, Message-ID: <20151118144534.DEAB42C0791@iredmail.druber.com>, mail_id: zlq7cOS-ZyIs, Hits: -0.001, size: 438, queued_as: 7B8572C06D6, 601 ms
Nov 18 09:45:35 iredmail postfix/smtp[12972]: DEAB42C0791: to=<dswartz@druber.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=0.63, delays=0.02/0/0/0.61, dsn=2.0.0, status=sent (250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as 7B8572C06D6)
Nov 18 09:45:35 iredmail postfix/qmgr[4173]: DEAB42C0791: removed
Nov 18 09:45:35 iredmail postfix/pipe[12980]: 7B8572C06D6: to=<dswartz@druber.com>, relay=dovecot, delay=0.05, delays=0/0/0/0.04, dsn=2.0.0, status=sent (delivered via dovecot service)
Nov 18 09:45:35 iredmail postfix/qmgr[4173]: 7B8572C06D6: removed

Mail from root on iredmail to outside address:

Nov 18 09:47:10 iredmail postfix/pickup[12775]: 90CA42C0791: uid=0 from=<root>
Nov 18 09:47:10 iredmail postfix/cleanup[12969]: 90CA42C0791: message-id=<20151118144710.90CA42C0791@iredmail.druber.com>
Nov 18 09:47:10 iredmail postfix/qmgr[4173]: 90CA42C0791: from=<root@druber.com>, size=450, nrcpt=1 (queue active)
Nov 18 09:47:15 iredmail postfix/smtpd[13068]: connect from iredmail.druber.com[127.0.0.1]
Nov 18 09:47:15 iredmail postfix/smtpd[13068]: CD3EB2C06D6: client=iredmail.druber.com[127.0.0.1]
Nov 18 09:47:15 iredmail postfix/cleanup[12969]: CD3EB2C06D6: message-id=<20151118144710.90CA42C0791@iredmail.druber.com>
Nov 18 09:47:15 iredmail postfix/qmgr[4173]: CD3EB2C06D6: from=<root@druber.com>, size=901, nrcpt=1 (queue active)
Nov 18 09:47:15 iredmail postfix/smtpd[13068]: disconnect from iredmail.druber.com[127.0.0.1]
Nov 18 09:47:15 iredmail amavis[11735]: (11735-04) Passed CLEAN {RelayedInbound}, <root@druber.com> -> <xxxxxxxxxxxx>, Message-ID: <20151118144710.90CA42C0791@iredmail.druber.com>, mail_id: F1jkPd9OzdpY, Hits: 0, size: 450, queued_as: CD3EB2C06D6, 5254 ms
Nov 18 09:47:15 iredmail postfix/smtp[12972]: 90CA42C0791: to=<xxxxxxxxxx>, relay=127.0.0.1[127.0.0.1]:10024, delay=5.3, delays=0.02/0/0/5.3, dsn=2.0.0, status=sent (250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as CD3EB2C06D6)
Nov 18 09:47:15 iredmail postfix/qmgr[4173]: 90CA42C0791: removed
Nov 18 09:47:16 iredmail postfix/smtp[13070]: Host offered STARTTLS: [smtpcorp.com]
Nov 18 09:47:17 iredmail postfix/smtp[13070]: CD3EB2C06D6: to=<xxxxxxxxxxxx>, relay=smtpcorp.com[216.22.15.245]:2525, delay=1.6, delays=0.01/0.04/0.6/1, dsn=2.0.0, status=sent (250 OK id=1Zz40z-NRKEsy-Dv)
Nov 18 09:47:17 iredmail postfix/qmgr[4173]: CD3EB2C06D6: removed

Mail from outside host to local address:

Nov 18 09:49:56 iredmail postfix/smtpd[13080]: connect from c7-b.mxthunder.net[208.53.48.218]
Nov 18 09:49:57 iredmail postfix/smtpd[13080]: 2D0CC2C06D6: client=c7-b.mxthunder.net[208.53.48.218]
Nov 18 09:49:57 iredmail postfix/cleanup[13089]: 2D0CC2C06D6: message-id=<BY1PR0801MB09036FA045ADA39D296C75D7921C0@BY1PR0801MB0903.namprd08.prod.outlook.com>
Nov 18 09:49:57 iredmail postfix/qmgr[4173]: 2D0CC2C06D6: from=<xxxxxx>, size=6399, nrcpt=1 (queue active)
Nov 18 09:49:57 iredmail postfix/smtpd[13080]: disconnect from c7-b.mxthunder.net[208.53.48.218]
Nov 18 09:49:58 iredmail postfix/smtpd[13094]: connect from iredmail.druber.com[127.0.0.1]
Nov 18 09:49:58 iredmail postfix/smtpd[13094]: 9F3BE2C0791: client=iredmail.druber.com[127.0.0.1]
Nov 18 09:49:58 iredmail postfix/cleanup[13089]: 9F3BE2C0791: message-id=<BY1PR0801MB09036FA045ADA39D296C75D7921C0@BY1PR0801MB0903.namprd08.prod.outlook.com>
Nov 18 09:49:58 iredmail postfix/qmgr[4173]: 9F3BE2C0791: from=<xxxxx>, size=6826, nrcpt=1 (queue active)
Nov 18 09:49:58 iredmail postfix/smtpd[13094]: disconnect from iredmail.druber.com[127.0.0.1]
Nov 18 09:49:58 iredmail amavis[11737]: (11737-04) Passed CLEAN {RelayedInbound}, [208.53.48.218]:61839 [157.56.111.108] <xxxxxx> -> <dswartz@druber.com>, Queue-ID: 2D0CC2C06D6, Message-ID: <BY1PR0801MB09036FA045ADA39D296C75D7921C0@BY1PR0801MB0903.namprd08.prod.outlook.com>, mail_id: fDbGgrt1Q0ou, Hits: 0.975, size: 6396, queued_as: 9F3BE2C0791, 1251 ms
Nov 18 09:49:58 iredmail postfix/smtp[13091]: 2D0CC2C06D6: to=<dswartz@druber.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=1.7, delays=0.37/0.03/0/1.3, dsn=2.0.0, status=sent (250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as 9F3BE2C0791)
Nov 18 09:49:58 iredmail postfix/qmgr[4173]: 2D0CC2C06D6: removed
Nov 18 09:49:58 iredmail postfix/pipe[13096]: 9F3BE2C0791: to=<dswartz@druber.com>, relay=dovecot, delay=0.07, delays=0.01/0.04/0/0.03, dsn=2.0.0, status=sent (delivered via dovecot service)
Nov 18 09:49:58 iredmail postfix/qmgr[4173]: 9F3BE2C0791: removed

So, what confuses you is the "Relayed{XXX}" tag? Quote from Amavisd-new release notes (http://www.ijs.si/software/amavisd/release-notes.txt )

- added a macro 'actions_performed', which expands into a comma-separated
  list of words: Accepted, Relayed(Untagged), RelayedTagged, Discarded,
  Rejected, Bounced, NoBounce or TempFailed, followed by a mail flow
  direction word: Inbound, Internal, Outbound or OpenRelay. For brevity
  the 'RelayedUntagged' status appears in this list as 'Relayed'.
  Additionally, the list may include words Quarantined and Archived.
  For multirecipient messages it is possible that the list includes
  more than one combination.

  The purpose of this macro is to augment the bare-bones 'Passed CLEAN'
  or 'Blocked SPAM' in the main log entry. For this purpose the default
  log template now includes this macro call. If the additional information
  is not desired in the log, please assign a customized template to the
  $log_templ configuration variable.

  Some examples of the new log entries:

    Passed CLEAN {RelayedOutbound}, ...
    Passed CLEAN {RelayedInbound}, ...
    Passed CLEAN {RelayedInternal,RelayedOutbound}, ...
    Passed SPAMMY {RelayedTaggedInbound}, ...
    Blocked SPAM {RejectedInbound,Quarantined}, ...
    Blocked INFECTED (Mal/BredoZp-B) {DiscardedInbound,Quarantined}, ...

  Semantics of entries in the 'actions_performed' list corresponds
  to the newly added SNMP variables 1.3.6.1.4.1.15312.2.1.1.19 - .26
  (with the exception that 'RelayedUntagged' counter is abbreviated
  in this macro as 'Relayed'). Please see their detailed description
  in a file AMAVIS-MIB.txt .

Excuse me, what's the real issue now?

I checked Amavisd source code (/usr/sbin/amavisd-new) to understand how it defines 'Relayed[XXX]':

      my $orig = $msginfo->originating;
      ...
      my $islocal = $r->recip_is_local;
        if ($orig) {
          if ($islocal) { $which_counts{$which.'Internal'}++ }
          else          { $which_counts{$which.'Outbound'}++ }
          $which_counts{$which.'Originating'}++;
        } else {
          if ($islocal) { $which_counts{$which.'Inbound'}++ }
          else          { $which_counts{$which.'OpenRelay'}++ }
        }
      ...

*) Mail was sent by an authenticated user, if recipient is a local user, it will be either RelayedInternal. otherwise RelayedOutbound.
*) Mail was sent by an external user (not authenticated), if recipient is a local user, it will be RelayedInbound. Otherwise RelayedOpenRelay.

Hope it helps.

If you have smtp authentication, it will be applied with both 'ORIGINATING' and MYNETS policy banks. if no smtp authentication, sending from 127.0.0.1 is 'MYNETS'.

I'm afraid that i may be not able to deeply/clearly explain how Amavisd works and how it detects 'internal', 'inbound', 'outbound', i suggest you ask in Amavisd mailing list to make it clear if it still confused you. Sorry about this.