Check a BIMI record, and whether the domain is in a state where it can actually work.
BIMI puts your logo beside your messages in supporting inboxes. It is the one piece of mail authentication with a visible reward, which is why marketing asks for it.
It also does nothing at all until DMARC is enforcing. A BIMI record on a domain sitting at p=none will sit there looking configured for months while no receiver ever shows the logo, and nothing tells you. That dependency is the single most useful thing a BIMI checker can report, so it is what this page leads with.
The second cost is the Verified Mark Certificate. Gmail will not display a logo without one, and a VMC is a paid annual certificate that requires a registered trademark on the mark itself. Plenty of domains publish BIMI, skip the VMC, and quietly get nothing at the receiver they cared about most.
For Gmail, yes. Some other receivers display a logo without one. If Gmail is where your audience is, the certificate is the real cost of BIMI and worth pricing before you start.
A square SVG, served over HTTPS, in the tiny profile BIMI specifies. A general-purpose SVG exported from a design tool will usually be rejected.