Manpage of mount_smbfs(8) states:
mount_smbfs [-E cs1:cs2] [-I host] [-L locale] [-M crights:srights] [-N]
[-O cowner:cgroup/sowner:sgroup] [-R retrycount] [-T timeout]
[-U username] [-W workgroup] [-c case] [-d mode] [-f mode]
[-g gid] [-n opt] [-u uid]
The option "-n opt" is never mentioned again or described/documented!
Further, the SMB (server message block) is outdated, the TCP port 139 used with NetBIOS is considered dangerous as it is an exploit to takeover windows connections. It has been recommended to disable using TCP/139.
I do not find ANY(!) hints how to use CIFS and TCP port 445 only! One can only guess that it is the addition to /user@server[:port1... with port1 substituted with 445.
Iit should be made clear whether mount_smbfs is a suitable tool to mount CIFS share from a CIFS only server.
In my experience, it is very hard to find any fitting FreeBSD documentation regarding CIFS. It seems this is already standard in the Linux world and I find it a pity that FreeBSD is behind, outdated or even worse incapable.
Just checked FreeBSD 12's man page and "-n opt" is still undescribed.