shell - command line sftp: email address as username -

i need connect sftp server mac os x , username given email address (someone@example.com)

so connection string looks like:

sftp someone@example.com@ftp.example.com

the connection not accept password assume confused double "@".

i tried escape first "@" "\@" crashed sftp server , have effect shell i'd think.

what proper way escape in order work.

unfortunately sftp command on mac os x not allow me option interactive username prompt.

add entry host in ~/.ssh/config has desired name.

host stupidadminhost     hostname ssh.example.com     user somewhere@outthere.com

then sftp stupidadminhost instead, no given username.

Expalin