Email subject with non ASCII char gives 550 Subject contains invalid characters (in hotmail)

[Antonio Garcia]

As it seems that nobody report this issue, may be it's only a bug in my code/config, but I would like to ask if someone detect this issue:

I my case, I checked in: EDGE and into an old 2.2M site but NOT in PHOENIX the following:
PHP: 5.6
Hosting in linux servers
Detected at least in admin/email.php (sending email from admin)

I detected that, in spanish sites when the subject comes with not ASCII chars, the emails:

- Are received by gmail.com recipients.
- Not reaches in xxx@hotmail.com. In my case, the sender email ([email protected]) receives a 'Mail delivery failed: returning message to sender' with the following error:

[email protected]
 host outbound.mailspamprotection.com [184.154.136.82]
 SMTP error from remote mail server after end of data:
 550 Subject contains invalid characters.

EDGE and 2.2m shares the same email.php class.

Tried to change:

$this->build_params['text_encoding'] = '7bit';

to

$this->build_params['text_encoding'] = 'base64';

with no success...

Anybody has the same issue?