The new PHP uses a newer version of OpenSSL. It appears that the encryption routine of the older OpenSSL is no longer natively supported by the newer OpenSSL, this has two effects (that we know of): Users get an error when logging in ("Ihr Anmeldekennwort wurde geändert. Bitte geben Sie Ihr altes Kennwort ein, um die Daten zu entschlüsseln.") and account switching is not possible. When logging into the primary account, not only does the system log into the associated IMAP account, but it also decrypts the passwords for the other linked IMAP accounts on the fly.