Blacklist Check — Whether Your Sending Addresses Are Listed
This checks the addresses behind your mail servers, and the domain itself, against a large set of public blocklists. Receiving servers consult these lists when deciding whether to accept, filter or reject a message, so a listing translates fairly directly into mail not arriving.
Why run it
Because you will not be told. There is no notification when a listing happens, and the effect is partial rather than total — some receivers consult the list you are on, others do not, so mail keeps flowing and just less of it arrives. Listings frequently have nothing to do with your behaviour: a shared hosting neighbour sent spam, an address was recycled from a previous owner with history, a compromised account sent a burst before anyone noticed. Delisting is usually straightforward once you know, and knowing is the entire problem.
Why automate it
Time on a list is damage taken. The cost is proportional to how long you remain listed, and the delisting process is typically quick — so the variable you actually control is detection latency. Checking on a schedule reduces that from however long until someone complains to a few hours. It also lets you correlate a listing with what happened just before it, which is usually how the underlying cause gets identified rather than merely cleared.
What it gives you
Early detection of a problem that has no internal symptoms and gets more expensive every day it goes unnoticed. Since remediation is fast and discovery is the bottleneck, monitoring is nearly all of the value.