Synology and QNAP email notifications with Microsoft 365

NAS units send some of the most important mail on the network: failed drives, degraded volumes, backup results, ransomware warnings. Both Synology DSM and QNAP QTS offer Microsoft 365 as a notification provider, but it depends on a personal sign-in and breaks when that person's password or MFA changes. The custom SMTP option, pointed at a relay on the LAN, is simpler and survives staff changes.

What the device needs

SMTP server: the SMTP-365 appliance's IP address, on your LAN.
Port: 2525 (or 25 if the device cannot change its port).
Authentication: none. Encryption: none. The relay is plain SMTP on the LAN and does the secure part to Microsoft itself.
Sender address: a real mailbox in your tenant (a shared "alerts" mailbox is free). The appliance can override it so every alert comes from the same address.
The device's address or subnet must be on the appliance's devices list (Settings → Devices).

Where the settings are

Synology DSM 7

Control Panel → Notification → Email: enable email notifications, Service provider = Custom SMTP server, SMTP server = the SMTP-365 appliance's IP address, Port = 2525, Secure connection (SSL/TLS) unchecked, Authentication required unchecked, Sender name and Sender email = the alerts mailbox, recipients as needed. Press Send a test email.

Synology DSM 6

Control Panel → Notification → E-mail: the same fields under Custom SMTP server.

QNAP QTS 5

Control Panel → Notification Center → Service Account and Device Pairing → E-mail → Add SMTP Service: Email account = Custom, SMTP server, Port 2525, Secure connection = None, no username or password, Sender address set. Then create a notification rule under Event Notifications.

QNAP QTS 4

Control Panel → System → Notification → E-mail: the same fields.

Backup applications on the NAS (Hyper Backup, Active Backup, Hybrid Backup Sync) use the same notification settings, so their reports arrive too.

If the test message does not arrive

What you see	Likely cause	Fix
Connection failed / cannot connect to server	Wrong relay address or port, or the device's subnet is not in the relay's allowed sources	Check the address and port; on the appliance, Settings → Devices, add the device's subnet
554 5.7.1 Relaying denied (or the connection closes at once)	The device's IP is not among the appliance's devices	Add the address or subnet under Settings → Devices on the appliance
Authentication or certificate error on the device	Authentication or TLS is still switched on in the device	Set authentication to none/off and SSL/TLS to off; the relay is plain SMTP on the LAN
Device says sent, nothing arrives	Delivery to Microsoft 365 failed and the job is held or failed	Open the appliance's Status page: held and failed jobs show the reason and can be re-queued
Arrives, but from the wrong address	The device's own From address is being used	Turn on the sender override on the appliance so every message is sent from the scanner mailbox

One appliance for all of them

The same SMTP-365 appliance that fixes the printers takes the UPS, the servers' management cards, the NAS and the phone system, on one licence with no per-device fees. Each device gets the same three settings and the appliance's Status page shows every message it handled. Background: what Microsoft changed.

Fix it once, for every device. SMTP-365 is a small appliance on your network that accepts plain SMTP from printers, UPSs, servers, NAS and phone systems and delivers it into your own Microsoft 365 tenant with modern authentication. One licence covers every device on the site. Download the free 30-day trial See pricing

Updated 2026-10-10. Menu names and screens vary between models and firmware versions; if yours differs, look for the same fields under the device's email, SMTP or notification settings. Corrections welcome at helpdesk@smtp-365.com.