A 250 OK response does not guarantee delivery to the Inbox. Gmail accepts the message, then applies post-acceptance filtering.
increase(smtp_550_5_7_1_total[5m]) > 10
: If more than 0.3% of recipients mark your emails as spam in Google Postmaster Tools , Gmail may start rejecting your messages outright. blocked emails gmail
Data lags by 7–14 days. No real-time.
