Troubleshoot: Outlook Error, Junk E-Mail List Limit

Symptoms

When you start Microsoft Outlook or when you try to configure your junk email settings, you may receive one of the following error messages:

Error message 1:

Cannot add to the server Junk E-mail Lists, you are over the size allowed on the server. The Junk E-mail Filter on the server will be disabled until your Junk E-mail Lists have been reduced to the size allowed by the server.
Would you like to manage your Junk E-mail Lists now?
Error message 2:

Unable to add to the server Junk E-mail Lists, you are over the size allowed on the server. The Junk E-mail Filter on the server will be disabled until your Junk E-mail Lists have been reduced to the size allowed by the server.
Would you like to manage your Junk E-mail Lists now?

Cause

Microsoft Exchange limits the space that's allotted to your various Junk E-mail lists. By default, this limit is 510 kilobytes (KB).

Considering this limit, there are four known causes of these errors:

You have a large number of entries in your Safe Senders, Blocked Senders, and Safe Recipients lists.

By default, you have a cumulative limit of 510 KB for all your Junk E-mail lists. If you have a large number of entries in these lists (cumulatively), you may receive one of these error messages when you try to add more items to the lists.
The Max Extended Rule Size registry value is incorrectly configured on the Exchange server.

Note

The Max Extended Rule Size registry value doesn't apply to Exchange Server 2013 and later versions.

On an Exchange server, you can configure the following registry data:

Registry key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
Value: Max Extended Rule Size
Type: DWORD
Data: an integer specifying the maximum size, in bytes, you want to allow for the junk e-mail rule

The value that you enter in the registry is interpreted as the maximum rule size in bytes. Therefore, if you want to specify a limit that's larger than the default 510 KB, you must enter a value greater than 522240 (decimal).

This error may occur when you unintentionally specify a value lower than the default limit. For example, you might enter a value of 1024 under the assumption that this is double the default limit of 510 KB. However, because the value is interpreted as the number of bytes, you have configured a limit of 1024 bytes, and this is substantially lower than the default limit of 510 KB.
The PR_RULE_MSG_STATE property of the Junk E-mail Rule message is incorrectly configured.

In an Exchange mailbox, your junk email settings are stored in a hidden message in the associated contents table of your Inbox folder. The subject of this hidden message is Junk E-mail Rule. This message has a PR_RULE_MSG_STATE property, and the default value of this property is 49 (decimal) or 0x31 (hexadecimal). If you disable junk email filtering in Outlook Web App, the value of this property becomes 48 (decimal) or 0x30 (hexadecimal). If the value that's specified for this property is something other than 48 or 49 (decimal), you may receive one of these error messages.
The Also trust e-mail from my Contacts option is enabled in Outlook.

On the Safe Senders tab of the Junk E-mail Options dialog box, you'll see the Also trust e-mail from my Contacts option. If this option is enabled, and you have a large number of contacts in your Contacts folder, you may unintentionally exceed the 510-KB limit on your mailbox. When this option is enabled, Outlook tries to add all the email addresses for your contacts to the Safe Senders list.

Below is a resolution guide for this error provided by Microsoft.
Outlook Junk Mail Error - Microsoft Help Article