need fully-qualified hostname

[tcurdt]

The delivery is failing for me because of the hostname.

To what is the fully-qualified hostname set in a container?
Can it be set with MAILNAME?

  758 delivering 1l7rgZ-0000CD-EJ
  758 R: dnslookup for tcurdt@foo.com
  759 T: remote_smtp for tcurdt@foo.com
  759 Connecting to spool.mail.gandi.net [217.70.178.1]:25 ... connected
  759   SMTP<< 220 spool.mail.gandi.net ESMTP Postfix
  759   SMTP>> EHLO 15b0717dc4c2
  759   SMTP<< 250-spool.mail.gandi.net
  759          250-PIPELINING
  759          250-SIZE 35651584
  759          250-ETRN
  759          250-STARTTLS
  759          250-ENHANCEDSTATUSCODES
  759          250-8BITMIME
  759          250 DSN
  759   SMTP>> STARTTLS
  759   SMTP<< 220 2.0.0 Ready to start TLS
  759   SMTP>> EHLO 15b0717dc4c2
  759   SMTP<< 250-spool.mail.gandi.net
  759          250-PIPELINING
  759          250-SIZE 35651584
  759          250-ETRN
  759          250-ENHANCEDSTATUSCODES
  759          250-8BITMIME
  759          250 DSN
  759   SMTP>> MAIL FROM:<> SIZE=3764
  759   SMTP>> RCPT TO:<tcurdt@foo.com>
  759   SMTP>> DATA
  759   SMTP<< 250 2.1.0 Ok
  759   SMTP<< 504 5.5.2 <15b0717dc4c2>: Helo command rejected: need fully-qualified hostname
  759   SMTP<< 554 5.5.1 Error: no valid recipients
  759   SMTP>> QUIT
  759   SMTP(close)>>
  758 LOG: MAIN
  758   ** tcurdt@foo.com R=dnslookup T=remote_smtp H=spool.mail.gandi.net [217.70.178.1] X=TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256 CV=no DN="CN=spool.mail.gandi.net": SMTP error from remote mail server after RCPT TO:<tcurdt@foo.com>: 504 5.5.2 <15b0717dc4c2>: Helo command rejected: need fully-qualified hostname
  758 LOG: MAIN
  758   Frozen (delivery error message)