Email parameters rejected by TestLink

[StephenP]

In TestLink 1.9.2 I get a message that there are security warnings.
In config_check.txt I see:
"Check following parameters of email feature:
tl_admin_email
from_email
return_path_email
smtp_host"

Based on the installation manual, I had specified all these values in custom_config.inc.php, along the lines given below (I have anonymised the e-mail addresses). But for some reason TestLink does not like them. Why might this be? What validation does TestLink do on these parameters?

$g_smtp_host = '192.168.0.200';
$g_tl_admin_email = 'redacted@example.com';
$g_from_email = 'testlink@example.com';
$g_return_path_email = 'redacted@example.com';

[fman]

config options are retrieved and search for string "_not_configured" is done on it's value

[StephenP]

So why would TestLink be giving me that message then? I'm using an editor with colour-coding, so I'm quite sure I haven't accidentally commented those lines out.

[StephenP]

Well, I've fixed the problem, even if I'm not sure what exactly it was. For some reason the config_check.txt file was not being updated. I deleted it and it was recreated without this error message. (Now I just have sort out why TestLink can't find the GD library.)