[horde] Help in configuring a webmail install to send / receive emails properly

[Louis-Philippe Allard]

Hello,

I am having a hard time getting a fresh webmail install to send & receive
emails to/from a Gmail account.

IMP is currently configured as my backend for Horde's authentication, and
IMP is configured  for IMAP retrieval of emails from my Gmail account with
this in /imp/config/backends.php

// IMAP server
$servers['imap'] = array(
    'disabled' => false,
    'name' => 'GMail IMAP Server',
    'hostspec' => 'imap.gmail.com',
    'hordeauth' => true,
    'protocol' => 'imap',
    'port' => 993,
    'secure' => 'ssl',
);

When I try to send an email with Horde, I ger a error popup saying "There
was an error sending your message: Sendmail error 127"

Sendmail is only used locally to send emails for system services, etc
(cron, alerts, smarttools, etc).. Not to be used for email communications.
This is why I want to use Gmail.  Anyways, it apprears as if my home IP was
on a blacklist for some email providers (namely hotmail) so using Gmail
will be more reliable.

/horde/config/conf.php has the following lines in it

$conf['mailer']['params']['sendmail_path'] = '/usr/lib/sendmail';
$conf['mailer']['params']['sendmail_args'] = '-oi';
$conf['mailer']['type'] = 'sendmail';

I tried to replace "sendmail" by smtp but I get "Cannot connect to SMTP
server" or such message.  What would be the best & most reliable way to
configure Horde globally to use Gmail exclusively for both authentication
AND email communications?

Thank you!