imap_open（）：无法打开流（imap ssl）

I'm trying to read emails from imap mail with the php library ddeboer/imap .

I've created a subdomain like this: abm.mydomain.be . The IMAP extension wasn't installed so I asked the server administrator to install it. The function imap_open now exists. But now I'm getting the following error:

AuthenticationFailedException in Server.php line 76:
Authentication failed for user abm@mydomain.be with error imap_open(): Couldn't open stream {mail.mydomain.be:993/imap/ssl/validate-cert}

The user and passwords are correctly (100% sure of that). When I check phpinfo I see the following with imap:

Does anyone knows what I'm doing wrong?