PHPMailer SMTP port 25 connection problem (10060) but same connection via Outlook successful - smtp

Question

Hello to the community.
I have come across a strange problem with PHPMailer.
I am trying to connect via SMTP to a host without encryption (port 25) and although I am able to connect to the said host via Outlook, the PHPMailer connection attempt fails with the message (10060):
Connection: opening to webmail.ypa.gr:25, timeout=300, options=array()<br>
2020-07-21 05:34:34 Connection failed. Error #2: stream_socket_client(): unable to connect to webmail.ypa.gr:25 (A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.) [...]<br>
2020-07-21 05:34:34 SMTP ERROR: Failed to connect to server: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond. (10060)<br>
SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting<br>
The parameters (host/port given by the server admins) set to PHPMailer ($EMAIL_CREDENTIALS) are dumped below.
array(9) {
["SMTP_HOST"]=>
string(14) "webmail.ypa.gr"
["SMTP_PORT"]=>
int(25)
["SMTP_AUTH"]=>
bool(true)
["SMTP_SECURE"]=>
bool(false)
["SMTP_AUTOTLS"]=>
bool(false)
["USERNAME"]=>
string(12) "..."
["PWD"]=>
string(6) "..."
["SENDER"]=>
string(12) "..."
["RECEIVER"]=>
string(12) "..."
}
This is the code snippet:
$mail = new PHPMailer(true);
var_dump($EMAIL_CREDENTIALS);
try
{
$mail->isSMTP();
$mail->SMTPDebug = 4;
$mail->Host = $EMAIL_CREDENTIALS["SMTP_HOST"];
$mail->Port = $EMAIL_CREDENTIALS["SMTP_PORT"];
$mail->SMTPAuth = $EMAIL_CREDENTIALS["SMTP_AUTH"];
$mail->SMTPSecure = $EMAIL_CREDENTIALS["SMTP_SECURE"];
$mail->SMTPAutoTLS = $EMAIL_CREDENTIALS["SMTP_AUTOTLS"];
$mail->Username = $EMAIL_CREDENTIALS["USERNAME"];
$mail->Password = $EMAIL_CREDENTIALS["PWD"];
$mail->setFrom($EMAIL_CREDENTIALS["SENDER"], "...");
$mail->addAddress($to);
$mail->Subject = $subject;
$mail->msgHTML($body);
$mail->send();
}
I have seen many answers to such problems but have not been able to fix it. Among others, I have explicitly disabled TLS.
Is there something else I can check?
Thank you.