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Synology SMB not working from iPhone: DSM 7.2 settings to check

By Isaac Griffiths, developer of SMBDrop ·

Synology NAS boxes are great SMB servers, and an iPhone can write to them directly. But DSM has a lot of SMB settings, and a few of them can quietly lock an iPhone out. This is the checklist I'd work through, in order, using the labels from Synology's own DSM 7 help pages.

If you haven't set the NAS up for iPhone access yet, start with how to back up iPhone photos to a Synology, which covers the shared folder and user from scratch. This page is for when that's done and it still won't work.

Where the settings live: Synology's help pages write the path as Control Panel → File Services → SMB → Advanced Settings. The help page itself is titled "SMB Settings", so the exact wording may differ slightly on your DSM version.

1. Use the NAS's local IP address, not QuickConnect

This catches a lot of people. Synology's help is clear: the SMB file service does not support QuickConnect addresses, so smb://yourid.quickconnect.to won't ever work. The same page says the Files app needs both devices on the same local network.

2. Check the SMB service and protocol range

  1. In Control Panel → File Services → SMB, make sure Enable SMB service is ticked.
  2. Open Advanced Settings → General.
  3. Set Maximum SMB protocol to SMB3.
  4. Set Minimum SMB protocol to SMB2.

That's Synology's own recommendation. A maximum lower than SMB3 has stopped iPhones connecting before. You may see advice online to set the minimum to SMB1; that was people working around an iPadOS 17 bug, and Synology "strongly advise[s] against using SMB1". Update iOS instead. More on that in the can't connect to server guide.

3. Set signing and transport encryption to Client defined

Two settings on the same General tab can refuse clients outright:

Apple doesn't document whether the Files app supports SMB signing or encryption, so I can't tell you for certain that Force breaks it. Client defined for both is the safe choice, because it leaves the decision to the client instead of turning clients away. Synology also notes that server signing "greatly reduces file transfer performance", which is worth knowing if transfers are slow.

4. Check Auto Block hasn't blocked your phone

From DSM 7.2, the SMB service supports Auto Block, which blocks IP addresses after too many failed sign-ins. Synology's article says Auto Block only blocks public IP addresses, so on a current build it shouldn't block your phone at home. A later SMB Service update says it was improved to avoid blocking addresses on the same subnet, which implies earlier builds could block local devices. So it's not a definite cause, but it takes a minute to check:

  1. Go to Control Panel → Security → Protection → Auto Block.
  2. Open the Allow/Block List and remove the iPhone's IP from the block list if it's there.
  3. Optionally, add your home network to the Allow List.

5. Check the firewall

If you've turned on DSM's firewall (Control Panel → Security → Firewall), make sure it allows SMB from your local network. Synology lists the ports as 137 to 139 and 445.

6. Check the user's privileges and folder permissions

If the account can write from a computer but the iPhone still shows it as read only, see the read-only share guide. I haven't found reports either way on whether Synology was affected by the iOS 18 read-only issue, so do these permission checks first.

7. Check the volume and folder are available

Synology's troubleshooting article says the volume's status has to be Normal, and an encrypted shared folder has to be mounted before anything can see it over SMB.

Other settings worth knowing about

Where SMBDrop fits

Disclosure: I make SMBDrop. It sends photos, videos and files from an iPhone straight into a Synology shared folder over SMB, and can import them back without overwriting anything on the phone. It talks to the same SMB service as the Files app, so every setting above applies to it as well. It doesn't use QuickConnect and doesn't find the NAS by itself: you enter the IP address and sign-in, then Find Shares lists the shared folders that user can reach. Away from home it works over a VPN such as Tailscale. Third-party apps, SMBDrop included, need Settings → Privacy & Security → Local Network switched on to reach the NAS. It's £9.99 once, no subscription, no account, iOS 17 or later. If you'd rather have a photo library on the NAS than plain folders, SMBDrop vs Synology Photos compares the two, and the Files app's limits explains when the free route is enough.

SMBDrop's Settings screen listing two saved SMB shares on a home NAS, with an Add SMB Share button

FAQ

Can I connect to my Synology from iPhone over SMB using QuickConnect?

No. Synology says the SMB file service doesn't support QuickConnect addresses. Use the NAS's local IP address at home, and a VPN with the NAS's VPN IP when you're away.

Which SMB protocol settings should a Synology use for iPhone?

Synology recommends Maximum SMB protocol set to SMB3 and Minimum SMB protocol set to SMB2. Don't lower the minimum to SMB1.

Should I set Synology server signing to Force?

Not while you're diagnosing. Synology says clients that don't support signing can't connect when it's set to Force, and Apple doesn't document how iOS handles signing. Try Client defined first.

Why did my Synology suddenly stop accepting connections from my iPhone?

It's worth checking Auto Block under Control Panel, Security, Protection. Synology says Auto Block only blocks public IP addresses, but older builds may have blocked local devices after too many failed sign-ins. If the iPhone's IP is on the block list, remove it and try again with the right password.

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