I keep getting SMTP errors like: 334 VXNlcm5hbWU6 UGFzc3dvcmQ6 Authentication unsuccessful [BL1PR13CA0304.namprd13.prod.outlook.com 2026-01-22T20:59:23.476Z 08DE59C2EA6C3D25]

and: '550 (x.x) [x.x.x.x]:xxxx is currently not permitted to relay through this server. Perhaps you have not logged into the pop/imap server in the last 30 minutes or do not have SMTP Authentication turned on in your email client.'

See also:

https://news.ycombinator.com/edit?id=46725075

https://news.ycombinator.com/item?id=46724812

https://www.reddit.com/r/msp/comments/1qk45c0/microsoft_serv...

https://www.reddit.com/r/sysadmin/comments/1qk3tg7/microsoft...

https://www.reddit.com/r/sysadmin/comments/1qk518l/email_ser...

What are my alternatives? We utilize the entire 365 suite and it feels daunting to migrate everything to individual services.