It is an empty FROM Address, this happens when an incoming email requests a notification of arrival/read, it'll reply with no FROM Address.

Afraid I'm not convinced for items like this reason... 

The iRedAdmin-Pro has blacklist options.  ? - web blacklist plugin.  Yet it seems to be failing. 

Example:  keep getting credit card offers from a group of IPs associated with this domain.   Yet the IPs of sending machine are in the list, the domain name is in the list, etc. and still accepts the mail. 

Received: from ajay152.downloadimage.info (ajay152.downloadimage.info [109.120.168.152])

DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; s=dkim; d=downloadimage.info;
h=To:Subject:Message-ID:Date:From:Reply-To:MIME-Version:List-Unsubscribe:Content-Type:Content-Transfer-Encoding; i=bounce@downloadimage.info;
bh=3hQqZoLdNZ5jBLoP0CNJJQwVrsQ=;
b=l4nTJ5GN2ZFRp8w17mU7DWDQ6syQ7pFKSKQHD+Y7WOUmR0D0zW8E+B7YM4Oebui0UClMdeWoYUfP
   asyuQaj3JZgAisd7s3cmhsuis5cq4edHsTZGSuwEqarpR6/6tMcyFdITdCwhOcIublGHEgHgLSDb
   aYJoshyyeh0SMLw9kDg=
DomainKey-Signature: a=rsa-sha1; c=nofws; q=dns; s=dkim; d=downloadimage.info;
b=dZbD/XwpNpk+jeC1J08BIWt5CgOAihuP2I9RL+BlS5bS9eT1MF+4d8yNxVl3lZyPoHSwHzfrJknv
   Fjcp1XJFf7Apj7+48N1ghoSrLVTG75WhFAmwsdgV8mHN4RFYcdBrcPW1wvOjvFekOcWRSjdPfs4h
   silVEVT4RQgkh3SOFYs=;

Assuming I understand correctly, this is one of the plugins (amavisd_wblist) in the settings.py file.
plugins = ['reject_null_sender', 'amavisd_wblist', 'sql_alias_access_policy', 'sql_user_restrictions']

2015-07-07 11:31:46 DEBUG Returned SQL Record: ('', '', '', '')
2015-07-07 11:31:46 DEBUG No recipient restriction.
2015-07-07 11:31:46 DEBUG <-- Result: DUNNO
2015-07-07 11:31:46 DEBUG Error while closing Amavisd database connection: AmavisdDBWrap instance has no attribute 'cursor'
2015-07-07 11:31:46 INFO [208.53.48.191] bounces+1605752-468f-user=domain_name.com@mail8.shared.hubspot.com -> user@domain_name.com, DUNNO
2015-07-07 11:31:46 DEBUG Session ended
2015-07-07 11:31:46 DEBUG Closed SQL connection.
2015-07-07 11:31:46 DEBUG smtp session: request=smtpd_access_policy
2015-07-07 11:31:46 DEBUG smtp session: protocol_state=RCPT
2015-07-07 11:31:46 DEBUG smtp session: protocol_name=ESMTP
2015-07-07 11:31:46 DEBUG smtp session: client_address=x.x.x.x
2015-07-07 11:31:46 DEBUG smtp session: client_name=5053c91.responsideexpension.link
2015-07-07 11:31:46 DEBUG smtp session: reverse_client_name=5053c91.responsideexpension.link
2015-07-07 11:31:46 DEBUG smtp session: helo_name=5053c91.responsideexpension.link
2015-07-07 11:31:46 DEBUG smtp session: sender=HomeSolarDeals@responsideexpension.link
2015-07-07 11:31:46 DEBUG smtp session: recipient=josh@domain_name.com
2015-07-07 11:31:46 DEBUG smtp session: recipient_count=0
2015-07-07 11:31:46 DEBUG smtp session: queue_id=
2015-07-07 11:31:46 DEBUG smtp session: instance=1974.559bf0e2.4fedc.0
2015-07-07 11:31:46 DEBUG smtp session: size=6956
2015-07-07 11:31:46 DEBUG smtp session: etrn_domain=
2015-07-07 11:31:46 DEBUG smtp session: stress=
2015-07-07 11:31:46 DEBUG smtp session: sasl_method=
2015-07-07 11:31:46 DEBUG smtp session: sasl_username=
2015-07-07 11:31:46 DEBUG smtp session: sasl_sender=
2015-07-07 11:31:46 DEBUG smtp session: ccert_subject=
2015-07-07 11:31:46 DEBUG smtp session: ccert_issuer=
2015-07-07 11:31:46 DEBUG smtp session: ccert_fingerprint=
2015-07-07 11:31:46 DEBUG smtp session: ccert_pubkey_fingerprint=
2015-07-07 11:31:46 DEBUG smtp session: encryption_protocol=
2015-07-07 11:31:46 DEBUG smtp session: encryption_cipher=
2015-07-07 11:31:46 DEBUG smtp session: encryption_keysize=0
2015-07-07 11:31:46 DEBUG --> Apply plugin: reject_null_sender
2015-07-07 11:31:46 DEBUG <-- Result: DUNNO
2015-07-07 11:31:46 DEBUG Creating Amavisd database connection.
2015-07-07 11:31:46 DEBUG Error while creating Amavisd database connection: (1045, "Access denied for user 'amavisd'@'localhost' (using password: YES)")
2015-07-07 11:31:46 DEBUG Skip plugin, error while getting db cursor: AmavisdDBWrap instance has no attribute 'cursor'
2015-07-07 11:31:46 DEBUG --> Apply plugin: sql_alias_access_policy
2015-07-07 11:31:46 DEBUG SQL: query access policy: SELECT accesspolicy, goto, moderators
            FROM alias
            WHERE
                address='josh@domain_name.com'
                AND address <> goto
                AND active=1
            LIMIT 1
   
2015-07-07 11:31:46 DEBUG SQL: record: None
2015-07-07 11:31:46 DEBUG <-- Result: DUNNO (Not mail alias)
2015-07-07 11:31:46 DEBUG --> Apply plugin: sql_user_restrictions
2015-07-07 11:31:46 DEBUG SQL to get restriction rules of sender (homesolardeals@responsideexpension.link):
        SELECT
            allowedrecipients, rejectedrecipients,
            allowedsenders, rejectedsenders
        FROM mailbox
        WHERE username='homesolardeals@responsideexpension.link'
        LIMIT 1
   
2015-07-07 11:31:46 DEBUG Returned SQL Record: None
2015-07-07 11:31:46 DEBUG SQL to get restriction rules of recipient (josh@domain_name.com):
            SELECT
                allowedrecipients, rejectedrecipients,
                allowedsenders, rejectedsenders
            FROM mailbox
            WHERE username='josh@domain_name.com'
            LIMIT 1
       
2015-07-07 11:31:46 DEBUG Returned SQL Record: ('', '', '', '')
2015-07-07 11:31:46 DEBUG No recipient restriction.
2015-07-07 11:31:46 DEBUG <-- Result: DUNNO
2015-07-07 11:31:46 DEBUG Error while closing Amavisd database connection: AmavisdDBWrap instance has no attribute 'cursor'
2015-07-07 11:31:46 INFO [76.74.216.217] HomeSolarDeals@responsideexpension.link -> josh@domain_name.com, DUNNO
2015-07-07 11:31:46 DEBUG Session ended
2015-07-07 11:31:46 DEBUG Closed SQL connection.

2015-07-07 11:37:37 DEBUG Returned SQL Record: ('', '', '', '')
2015-07-07 11:37:37 DEBUG No recipient restriction.
2015-07-07 11:37:37 DEBUG <-- Result: DUNNO
2015-07-07 11:37:37 DEBUG Error while closing Amavisd database connection: AmavisdDBWrap instance has no attribute 'cursor'
2015-07-07 11:37:37 INFO [70.39.66.198] info@debsurfed.com -> user@domain_name.com, DUNNO
2015-07-07 11:37:37 DEBUG Session ended
2015-07-07 11:37:37 DEBUG Closed SQL connection.
2015-07-07 11:37:38 DEBUG Connect from 127.0.0.1, port 38014.
2015-07-07 11:37:38 DEBUG smtp session: request=smtpd_access_policy
2015-07-07 11:37:38 DEBUG smtp session: protocol_state=RCPT
2015-07-07 11:37:38 DEBUG smtp session: protocol_name=ESMTP
2015-07-07 11:37:38 DEBUG smtp session: client_address=x.x.x.x
2015-07-07 11:37:38 DEBUG smtp session: client_name=mail-ig0-f177.google.com
2015-07-07 11:37:38 DEBUG smtp session: reverse_client_name=mail-ig0-f177.google.com
2015-07-07 11:37:38 DEBUG smtp session: helo_name=mail-ig0-f177.google.com
2015-07-07 11:37:38 DEBUG smtp session: sender=doug+caf_=user=domain_name.com@marcshomes.net
2015-07-07 11:37:38 DEBUG smtp session: recipient=user@domain_name.com
2015-07-07 11:37:38 DEBUG smtp session: recipient_count=0
2015-07-07 11:37:38 DEBUG smtp session: queue_id=
2015-07-07 11:37:38 DEBUG smtp session: instance=1b96.559bf242.44037.0
2015-07-07 11:37:38 DEBUG smtp session: size=5900
2015-07-07 11:37:38 DEBUG smtp session: etrn_domain=
2015-07-07 11:37:38 DEBUG smtp session: stress=
2015-07-07 11:37:38 DEBUG smtp session: sasl_method=
2015-07-07 11:37:38 DEBUG smtp session: sasl_username=
2015-07-07 11:37:38 DEBUG smtp session: sasl_sender=
2015-07-07 11:37:38 DEBUG smtp session: ccert_subject=
2015-07-07 11:37:38 DEBUG smtp session: ccert_issuer=
2015-07-07 11:37:38 DEBUG smtp session: ccert_fingerprint=
2015-07-07 11:37:38 DEBUG smtp session: ccert_pubkey_fingerprint=
2015-07-07 11:37:38 DEBUG smtp session: encryption_protocol=TLSv1.2
2015-07-07 11:37:38 DEBUG smtp session: encryption_cipher=ECDHE-RSA-AES128-GCM-SHA256
2015-07-07 11:37:38 DEBUG smtp session: encryption_keysize=128
2015-07-07 11:37:38 DEBUG --> Apply plugin: reject_null_sender
2015-07-07 11:37:38 DEBUG <-- Result: DUNNO
2015-07-07 11:37:38 DEBUG Creating Amavisd database connection.
2015-07-07 11:37:38 DEBUG Error while creating Amavisd database connection: (1045, "Access denied for user 'amavisd'@'localhost' (using password: YES)")
2015-07-07 11:37:38 DEBUG Skip plugin, error while getting db cursor: AmavisdDBWrap instance has no attribute 'cursor'
2015-07-07 11:37:38 DEBUG --> Apply plugin: sql_alias_access_policy
2015-07-07 11:37:38 DEBUG SQL: query access policy: SELECT accesspolicy, goto, moderators
            FROM alias
            WHERE
                address='user@domain_name.com'
                AND address <> goto
                AND active=1
            LIMIT 1
   
2015-07-07 11:37:38 DEBUG SQL: record: None
2015-07-07 11:37:38 DEBUG <-- Result: DUNNO (Not mail alias)
2015-07-07 11:37:38 DEBUG --> Apply plugin: sql_user_restrictions
2015-07-07 11:37:38 DEBUG SQL to get restriction rules of sender (doug+caf_=user=domain_name.com@marcshomes.net):
        SELECT
            allowedrecipients, rejectedrecipients,
            allowedsenders, rejectedsenders
        FROM mailbox
        WHERE username='doug+caf_=user=domain_name.com@marcshomes.net'
        LIMIT 1
   
2015-07-07 11:37:38 DEBUG Returned SQL Record: None
2015-07-07 11:37:38 DEBUG SQL to get restriction rules of recipient (user@domain_name.com):
            SELECT
                allowedrecipients, rejectedrecipients,
                allowedsenders, rejectedsenders
            FROM mailbox
            WHERE username='user@domain_name.com'
            LIMIT 1
       
2015-07-07 11:37:38 DEBUG Returned SQL Record: ('', '', '', '')
2015-07-07 11:37:38 DEBUG No recipient restriction.
2015-07-07 11:37:38 DEBUG <-- Result: DUNNO
2015-07-07 11:37:38 DEBUG Error while closing Amavisd database connection: AmavisdDBWrap instance has no attribute 'cursor'
2015-07-07 11:37:38 INFO [209.85.213.177] doug+caf_=usern=domain_name.com@marcshomes.net -> user@domain_name.com, DUNNO
2015-07-07 11:37:38 DEBUG Session ended
2015-07-07 11:37:38 DEBUG Closed SQL connection.

Yes, will do. Thank you!

Does that map to amavisd database, users table? 

Back later with update as out for few.

Thanks. 

So does the settings.py map to the mysql database, user: amavid/password or is this value in different database/location?

Hello,
My apologies for making this more complex than it really should be.  However, I'm not clear on what your stating to set the password too, so please bear with me as I try to communicate it more clearly. 

I've looked at the settings.py and the sample file.  They do both reflect what appears to be the database as follows:
amavisd_db_name = "amavisd"
amavisd_db_user = "amavisd"
amavisd_db_password = "Correct_Password_Value"

That being said, I understand the process to be the following steps.  Would you please correct any errors on my part?
Step 1) Locate the correct database password in MySQL.
Step 2) Insert this value into the amavisd_db_password = "Correct_Password_Value" for the database connection in the settings.py file.
Step 3) Restart the service: iredapd.   

So, in looking in MySQL for the correct database password, I first thought the database password value would be in amavisd database.  However, there is No amavisd user or password in any table of that database.  I could have made a mistake somewhere, but I cannot locate any amavisd user in ANY of the databases/tables OTHER than MySQL itself (amavisd, vmail, etc.).   

Where do I locate the correct amavisd password from MySQL to insert into the settings.py file? 

Additional questions/concerns as result of this:
The amavisd database table: users
a) seem to have values which I find confusing (as possibly wrong).  Those values appear to possibly be related to some of the standard email users on the system.  Does that sound correct?

b) Also in the 'users" table is a value of "@." in the email column.  Should this be in the table?  I ask because the iRedAdmin-Pro web interface page (Whitelists & Blacklists:https://some_domain/iredadmin/system/wblist)  implies that the value of "@." would result in "ALL accounts" possibly being blocked.  So, is this intended to say all email will be blocked?

Yes remember that file and it has a value.  However, this system was maintained by another person and has had two upgrades (performed by you) so I did not think that file would be accurate today.    Thanks for the tip/tips :-)

Ironically, I also looked in the original "config" file which is also archived on the system.  It has a value which I just tried.  if understanding the logs, it is working now without any db_connection errors at this time.  The value does in fact match the iRedMail.tips file value as well.  So, it appears to have NOT been altered. 
Example:
2015-07-08 12:27:18 DEBUG smtp session: encryption_cipher=
2015-07-08 12:27:18 DEBUG smtp session: encryption_keysize=0
2015-07-08 12:27:18 DEBUG --> Apply plugin: reject_null_sender
2015-07-08 12:27:18 DEBUG <-- Result: DUNNO
2015-07-08 12:27:18 DEBUG Creating Amavisd database connection.
2015-07-08 12:27:18 DEBUG Got db cursor.
2015-07-08 12:27:18 DEBUG --> Apply plugin: amavisd_wblist
2015-07-08 12:27:18 DEBUG Possible policy senders: ['@.', 'fernanda@speedjon.com', '@speedjon.com', '@.speedjon.com', '@com', '@.com', '82.211.35.173', '82.*.*.*', '*.*.*.173', '82.*.35.173', '82.211.35.*', '82.211.*.173', '*.211.35.173', '82.*.*.173', '*.*.35.173', '*.*.*.*', '82.211.*.*']

This still never answered the question as to where in the MySQL database said password lives.  Are you not willing to share where that value resides in the database?  Was I correct and that is just the hashed string of the plain text string?

Great, I will read it today.  However, I'm getting an error when following the link.  Maybe it is not published live yet? 

Agreed.  Watching the iredapd.log via debug mode now.  Testing some inbound e-mail which appears to be arriving.

Dashboard does in fact show Top 10 with "<>" user as high user for the existing period.
I'm thinking that:
   The db connection failure was resulting in system NOT blocking "null user"
   That if corrected the null user block should start taking place now.

Once published and read by me, what else do you recommend to investigate?

Thank you for the replies & help!

It worked and is now visible. 

Yes, updated the previous with this snippet.

2015-07-08 12:27:18 DEBUG smtp session: encryption_cipher=
2015-07-08 12:27:18 DEBUG smtp session: encryption_keysize=0
2015-07-08 12:27:18 DEBUG --> Apply plugin: reject_null_sender
2015-07-08 12:27:18 DEBUG <-- Result: DUNNO
2015-07-08 12:27:18 DEBUG Creating Amavisd database connection.
2015-07-08 12:27:18 DEBUG Got db cursor.
2015-07-08 12:27:18 DEBUG --> Apply plugin: amavisd_wblist
2015-07-08 12:27:18 DEBUG Possible policy senders: ['@.', 'fernanda@speedjon.com', '@speedjon.com', '@.speedjon.com', '@com', '@.com', '82.211.35.173', '82.*.*.*', '*.*.*.173', '82.*.35.173', '82.211.35.*', '82.211.*.173', '*.211.35.173', '82.*.*.173', '*.*.35.173', '*.*.*.*', '82.211.*.*']