I was trying to configure mantisbt to send mail nofitications, using this configuration:

$g_phpMailer_method = PHPMAILER_METHOD_SMTP;
$g_smtp_host = 'smtp.dreamhost.com';
$g_smtp_username = 'envios@cordoba.cc';
$g_smtp_password = 'password';
$g_smtp_port = '587';
$g_smtp_connection_mode = 'tls';
$g_administrator_email = 'envios@cordoba.cc';
$g_webmaster_email = 'envios@cordoba.cc';
$g_from_email = 'envios@cordoba.cc'; # the "From: " field in emails
$g_return_path_email = 'envios@cordoba.cc'; # the return address for bounce>
$g_from_name = 'Mantis Bug Tracker';
$g_enable_email_notification = ON;

It didn't works, and checking my SMTP server logs, I found that it was trying to authenticate using CRAM-MD5, whereas using plain text password was the intended.

After diving a bit into MaintsBT, I found that $t_mail->AuthType (property of PHPMailer class) is never set, and seems to default to CRAM-MD5. So I solved my problem by hardcoding a new line in core/email_api.php between lines 1310 and 1311:

$t_mail->AuthType = 'PLAIN';

It worked like a charm, and I started receiving emails.

Maybe I have missed some code where the AuthType is handled, but in case I haven't, a new parameter to handle this should be implemented to make sending mail feature compatible with SMTP servers that does not support CRAM-MD5.