Fix "550 5.7.30 Basic authentication is not supported for Client Submission"

This bounce means the device or app logged in to Exchange Online SMTP with a username and password, and the tenant no longer accepts that. The message was not sent and will not be retried.

Why it happens

Microsoft is retiring basic authentication for SMTP client submission (see the timeline). The error appears when basic auth is disabled for the tenant or for that mailbox.

Fix 1: re-enable it (temporary)

An Exchange administrator can allow SMTP AUTH for the mailbox again, for as long as Microsoft still allows it:

Connect-ExchangeOnline
Set-CASMailbox -Identity scanner@yourdomain.com -SmtpClientAuthenticationDisabled $false

If the tenant-wide setting blocks it, check Get-TransportConfig | Format-List SmtpClientAuthenticationDisabled. Security defaults and Conditional Access policies that block legacy authentication also cause this error. This buys time until Microsoft's final removal date.

Fix 2: move the device to SMTPKeep (permanent)

Point the device at SMTPKeep instead of smtp.office365.com. It still logs in with a simple username and password, but to SMTPKeep, which then sends through your mailbox with Microsoft Graph and OAuth. Settings:

SMTP server	`smtp.smtpkeep.com`
Port	`587`
Security	STARTTLS (may be labelled TLS, "Use SSL/TLS: STARTTLS" or "Secure connection")
Authentication	SMTP AUTH on, username and password from the SMTPKeep dashboard
From / device email address	The mailbox you chose for the device, for example `scanner@yourdomain.com`
Older devices	If the device only supports TLS 1.0 or 1.1, use port `2525` instead

See the copier setup guide for where these fields are on common brands.