[Info-vax] $ mail/subj="test" NL: smtp%"John.Doe at gmail.com" failed

[DTL]

Hello,

I enabled my SMTP Client for

  DIGITAL TCP/IP Services for OpenVMS Alpha Version V5.6
  on a DEC 3000 Model 400 running OpenVMS V8.3

but command 

$  mail/subj="test" NL: smtp%"John.Doe at gmail.com" 

failed "gracefully" (no error messages on screen)
Mail did not go through.
I checked my spam box, nothing.
Where should I start my investigations, please?
Thanks.

Didier