If your mail server uses LDAP or Active Directory, we recommend using that and disabling the catch-all feature: Using Active Directory (Exchange) or LDAP to set up valid email addresses
Without the catch-all feature, you would need to maintain a list of valid email recipients that SpamHero should accept mail for, and any email for an address you do not add in the SpamHero control panel would be rejected.
However, when you have the catch-all feature enabled, SpamHero will accept mail for all possible email addresses for your domain, so you do not have to maintain a list of valid addresses.
The catch-all feature is enabled by default on all domains, but can be disabled if you choose.
If you find that you are receiving a large amount of messages for invalid recipients that are causing your account to go over the message limit and receive overage charges, you may want to consider disabling the catch-all, as messages to unknown recipients will no longer count against your total when the catch-all is disabled.
For most cases, however, leaving the catch-all on is not likely to lead to overage charges on its own.
When the catch-all feature is enabled, any messages sent to a recipient that our system has not seen before will be initially deferred (also known as "greylisting". When email is coming from a valid sender, the sending server will automatically immediately retry the message resulting in a very brief delay in delivery for the first message sent to a new recipient (usually less than a minute).
Because spammer's mail servers are focused on sending email very fast to as many users as possible, they will usually skip recipients with greylisting enabled. This protects your domain from having a bunch of invalid email addresses added as recipients in SpamHero, especially when a spammer executes a dictionary attack against your domain.
Disabling the catch-all feature will also disable greylisting automatically. If you wish to leave the catch-all enabled but want greylisting disabled, contact our support team for assistance. Be aware that having greylisting disabled while the catch-all is enabled may result in a large number of invalid email addresses being detected as valid.
If a single recipient listed on an email is unrecognized, the message will be greylisted. If there are multiple unrecognized recipients, the delivery of the message can be delayed significantly.