Greylist Filters

As covered in detail on the Antispam | Options page, greylisting works by temporarily rejecting mail from any sending IP, sender address and recipient address combination that SmarterMail hasn't seen before, on the assumption that legitimate mail servers will retry the delivery a short time later while most spam sources will not. This page, Greylist Filters, is not where greylisting itself is turned on or tuned — that's handled by the Block Period, Pass Period, Record Expiration and related settings on the Options page. Instead, this page maintains a list of specific IP addresses and countries that should always be exempt from greylisting, regardless of whether SmarterMail has seen that sender before.

How Greylist Filters relate to other exemptions

The Options page's Greylisting Options section notes that several categories of mail are already exempt from greylisting: SMTP whitelisted IPs, Whitelist entries with Bypass Greylisting enabled, anyone who authenticates, trusted senders, and anyone who has already passed greylisting once before. The filters on this page are simply another entry in that same list of exemptions — functionally, a match here is treated no differently than a match against any of those other categories. If an incoming message's sending IP address, or the country that IP resolves to, matches an entry in the Greylist Filters grid, greylisting is skipped entirely for that message and it proceeds directly to normal spam processing. There is no separate precedence or ordering to worry about between this list and the other exemption types — a match on any one of them is sufficient.

Note: A Greylist Filter only ever works in one direction. Adding an entry here always means "never greylist mail from this IP address or country" — there is no option on this page to configure a filter that greylists a specific IP or country more aggressively, or that forces greylisting to apply where it otherwise wouldn't. If you need to be more restrictive with mail from a particular source, that's accomplished through other antispam tools (RBLs, SMTP Blocking, custom spam checks, etc.), not through this page.

Adding or Editing a Greylist Filter

To add a new IP address or country code exemption, click New. To edit an existing filter, click on it from the list. The following fields are available:

Filter Type - Select the type of filter you want to add: IP Address or Country Code. Only the field that corresponds to the selected type (described below) needs to be filled in.
IP Address - Available when Filter Type is set to IP Address. Enter the IP address that should be exempt from greylisting. This field accepts a single IP address (e.g., 203.0.113.15) or a range of addresses in CIDR notation (e.g., 203.0.113.0/24), so an entire block belonging to a partner or upstream relay can be exempted with a single entry instead of one filter per address.
Country Code - Available when Filter Type is set to Country Code. Select a country from the list. Every message whose sending IP address is identified as originating from that country will bypass greylisting, regardless of the specific IP involved.
Description - A friendly name or descriptor for the filter, useful for identifying its purpose later at a glance. For example, Contoso EDI Server or Microsoft 365.

How country codes are determined

Country Code filters rely on SmarterMail resolving a sending IP address to a country. SmarterMail first checks the IP against its own internal geolocation database. If the address isn't found there, SmarterMail falls back to a reverse DNS lookup on the IP and inspects the resulting hostname's top-level domain (for example, a hostname ending in .de would be treated as Germany). Because both the geolocation database and the reverse-DNS fallback are approximations — ISPs reassign IP blocks, and not every hostname's TLD reflects the country it's actually hosted in — a Country Code filter can occasionally fail to match (or incorrectly match) a handful of edge-case IP addresses. This is worth keeping in mind if a specific message from an otherwise qualifying country unexpectedly still gets greylisted.

Examples

Exempting a partner's static IP range: Suppose a business partner sends time-sensitive order confirmations from a fixed block of servers, such as 198.51.100.0/24, and the several-minute delay introduced by greylisting's initial temporary failure is causing those confirmations to arrive later than desired. Adding a Greylist Filter with Filter Type IP Address, IP Address 198.51.100.0/24, and Description Partner EDI Range ensures every message from that block is delivered immediately, without waiting on the sending server to retry.
Exempting an entire country a partner operates from: If a company works with numerous vendors and government offices throughout, for example, Canada, and finds that mail from those organizations is frequently delayed because it originates from a wide, ever-changing set of Canadian ISP IP addresses (making individual IP filters impractical to maintain), adding a Greylist Filter with Filter Type Country Code and Country Code CA exempts all mail identified as coming from Canada, without having to track individual sending IPs.

Built-in (Internal) Filters

Some greylist filters are included by default and cannot be modified or removed by an administrator. These default filters are indicated in the grid by a checkmark in the Internal column. Out of the box, the default filters cover two categories:

Private/loopback address ranges — 127.0.0.1, ::1, 192.168.0.0/16, 10.0.0.0/8, and 172.16.0.0/12 — so that internal, loopback, or LAN-originated mail is never delayed by greylisting.
Sending IP ranges published by a handful of major mail providers, including Outlook.com (and its Germany endpoints), Hotmail.com (and its Germany endpoints), Office 365 (Exchange Online), Gmail and Google Workspace, Yahoo!, AOL.com, Amazon.com (and Amazon Cloud), eBay, and Steam. SmarterMail builds this portion of the default list by looking up each provider's published SPF sending IPs at the time the filters are first generated (either on initial installation or whenever antispam settings are reset from the Options page's Actions (⋮) menu).

Note: Because the major-provider entries above are captured from each provider's SPF records at the time the defaults were generated, they reflect a snapshot rather than a continuously updated feed. If a provider changes its sending IP ranges after your server's defaults were created, the built-in filter won't automatically pick up the change unless the antispam settings are reset again. If mail from one of these providers is unexpectedly greylisted, consider adding your own (non-internal) IP Address or Country Code filter as a supplement rather than waiting on the built-in entry to update.