Gmail's spam detection has some real headscratcher moments every now and then.
Some days it'll mark legitimate transaction emails from major companies as spam even if you've been receiving emails from them for years.
And then right afterwards it'll allow an obvious scam email with a PDF attachment from some random Gmail account that you've never contacted to go straight to your inbox.
It's gotten to the point that I don't open emails from Sendgrid support because 4 out of 5 are poorly disguised phishing attempts.
Several years back when I applied for a Google internship, I missed some emails from my recruiter ([email protected]) because they went to my gmail spam folder.