Sendmail use localhost.localdomain

Sendmail with Perl uses localhost.localdomain instead of a fully qualified domain name (FQDN). Sendmail and server configuration is correct, hostname is setup with FQDN.

My script contains the following lines:

use MIME::Lite;
use Email::Sender::Simple qw /sendmail/;
use Email::Sender::Transport::SMTPS;

...

my $transport = Email::Sender::Transport::SMTPS->new({
  host          =>  $server,
  ssl           => 'starttls',
  port          =>  $port,
  sasl_username =>  $user,
  sasl_password =>  $password,
  debug         =>  1,
});

sendmail($msg->as_string, { transport => $transport });

Mail is sent successfully, however sendmail use localhost.localdomain instead of FQDN with EHLO. Debug information shows:

Net::SMTPS>>> Net::SMTPS(0.09)
Net::SMTPS>>>   IO::Socket::IP(0.39)
Net::SMTPS>>>     IO::Socket(1.40)
Net::SMTPS>>>       IO::Handle(1.40)
Net::SMTPS>>>         Exporter(5.73)
Net::SMTPS>>>   Net::SMTP(3.11)
Net::SMTPS>>>     Net::Cmd(3.11)
Net::SMTPS=GLOB(0x2903e48)<<< 220 smtp.gmail.com ESMTP l186sm18879092ioa.54 - gsmtp
Net::SMTPS=GLOB(0x2903e48)>>> EHLO localhost.localdomain
Net::SMTPS=GLOB(0x2903e48)<<< 250-smtp.gmail.com at your service, [masked IP address]
Net::SMTPS=GLOB(0x2903e48)<<< 250-SIZE 35882577
Net::SMTPS=GLOB(0x2903e48)<<< 250-8BITMIME
Net::SMTPS=GLOB(0x2903e48)<<< 250-STARTTLS
Net::SMTPS=GLOB(0x2903e48)<<< 250-ENHANCEDSTATUSCODES
Net::SMTPS=GLOB(0x2903e48)<<< 250-PIPELINING
Net::SMTPS=GLOB(0x2903e48)<<< 250-CHUNKING
Net::SMTPS=GLOB(0x2903e48)<<< 250 SMTPUTF8
Net::SMTPS=GLOB(0x2903e48)>>> STARTTLS
Net::SMTPS=GLOB(0x2903e48)<<< 220 2.0.0 Ready to start TLS
Net::SMTPS=GLOB(0x2903e48)>>> EHLO localhost.localdomain
Net::SMTPS=GLOB(0x2903e48)<<< 250-smtp.gmail.com at your service, [masked IP address]
Net::SMTPS=GLOB(0x2903e48)<<< 250-SIZE 35882577
Net::SMTPS=GLOB(0x2903e48)<<< 250-8BITMIME
Net::SMTPS=GLOB(0x2903e48)<<< 250-AUTH LOGIN PLAIN XOAUTH2 PLAIN-CLIENTTOKEN OAUTHBEARER XOAUTH
Net::SMTPS=GLOB(0x2903e48)<<< 250-ENHANCEDSTATUSCODES
Net::SMTPS=GLOB(0x2903e48)<<< 250-PIPELINING
Net::SMTPS=GLOB(0x2903e48)<<< 250-CHUNKING
Net::SMTPS=GLOB(0x2903e48)<<< 250 SMTPUTF8

When sendmail is used from the console directly (not using Perl), correct FQDN is used with EHLO.

Solution

Net::SMTPS=GLOB(0x2903e48)>>> EHLO localhost.localdomain

From the documentation of Email::Sender::Transport::SMTPS:

ATTRIBUTES
The following attributes may be passed to the constructor:
...
helo: what to say when saying HELO; no default

If nothing is given in helo the default from the underlying packet (Net::SMTPS) is used, which is localhost.localdomain. To use something different just do

my $transport = Email::Sender::Transport::SMTPS->new({
    ...,
    helo => 'whatever.you.want.to.use.instead.of.localhost.localdomain'
});