By default, only people on your team can email bills into your AP inbox. If you work with a vendor who sends invoices regularly, you can let that vendor email invoices straight in, so each one becomes a draft bill without anyone on your team forwarding it.
This is an exception you grant on purpose, one vendor at a time. It lets an outside sender create draft bills in your account, so turn it on only for vendors you know and expect invoices from. It is an admin setup, and most teams do not need it.
When to use it
Setting this up for a vendor is worth it when:
They invoice you often, so forwarding each one by hand adds up.
Their invoices come from a consistent email address.
You would rather their bills appear as drafts automatically than rely on someone to forward them.
For a vendor you pay once or only now and then, skip it. It is simpler to have a team member forward the invoice in, which needs no setup. See Send a bill by email.
How a vendor is trusted
ImpactGraph is default-deny: it creates a draft only from senders it trusts, and everyone outside your team starts untrusted. When you allow a vendor, ImpactGraph accepts invoices that come from the email on file as that vendor's account holder. A message from any other address is rejected, even for an allowed vendor, so the invoice has to come from the address you have on record.
Your inbox also has to be on. If the Accept inbound email switch in Bill Pay settings is off, no outside mail is accepted, no matter which vendors you have allowed.
Turn it on for a vendor
Open the vendor's record and go to its edit form.
Turn on Allow inbound email.
Check that the email on file for the vendor matches the address they will send from.
Invoices from that vendor's account-holder email now become draft bills automatically. Turn the toggle off any time to stop accepting their email.