Encrypted IMAP connections to mail.cs.helsinki.fi mail server failed for most email programs.

A new IMAP  server certificate had been installed, but the certificate authority (CA) which had signed the new certificate is not a root CA itself (TERENA SSL CA), but an intermediate CA, which is then signed by a genuine root CA (UTN-USERFirst-Hardware). The IMAP server did not return the intermediate CA to email clients, which caused certificate validation to fail for most email programs.

This has since been fixed and mail.cs.helsinki.fi imap server now correctly returns the whole certificate chain.