Normally if server down, smtp will wait a little while and try again.

Nah, no way they're getting rid of their M.C.-Escher-esque 'Forefront' mail-disappearance-machine-that-nobody-in-Microsoft-seems-to-understand-or-control, but, yeah, even their Internet-facing infrastructure seems unhappy:

451 4.3.2 Temporary server error. Please try again later ATTR2 [MI3PEPF00008486.eurprd02.prod.outlook.com 2026-11-12Txxxxxxxxxxxxxx]

Anything sent to my work or home Outlook email from gmail doesn't bounce back, and anything sent from those is still stuck in the outbox. Microsoft.