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While the cifs:// approach has been a common past suggestion there is a settings file you can edit in OS X to tell OS X to use a specific version of SMB.I suggest you do the following in Terminal.app to find out more details about this.man nsmb.confNote: The nsmb.conf file can be in one of two locations it can be at ~/Library/Preferences/nsmb.conf or it can be at /etc/nsmb.conf as standard neither will initially exist and therefore the default settings - in this case first trying SMB3 will apply. Only if you create a file in one of these locations will it take effect. The /etc/nsmb.conf if it exists overrides any individual users copy.Note: nsmb.conf controls settings where your Mac is the SMB client and is connecting to another SMB server. A different file controls settings where the Mac is the SMB server, this is /Library/Preferences/SystemConfiguration/com.apple.smb.server.plistA second related issue that was introduced with El Capitan was the new requirement that packet signing be used, i.e. the default setting is that the client connecting to your Mac must now support packet signing. Some older multi-function printers in particular do not support this. Other than updating the firmware of such printers it is also possible to turn this setting off in OS X as below.sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.smb.server SigningRequired falseThis would not affect Macs connecting to other SMB servers only when a SMB client tries connecting to the Mac, therefore I do not believe it should be relevant to your issue.Note: Windows has supported packet signing for a very long time.*https://discussions.apple.com/thread/7427556