A new Debian security update was released this morning for Dovecot, the IMAP & POP3 server which Symbiosis uses. Unfortunately this caused problems for Symbiosis, denying all logins.
We previously listed instructions here for downgrading and restarting the service - but Debian have now released an update which reverses the regression which was introduced in this security update.
To resolve the problem now you should only need to run:
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install symbiosis-email
This will install version
1:2.2.13-12~deb8u3 of the various
dovecot-* packages. You can confirm that, post-upgrade, via:
dpkg --list | egrep "(dovecot|email)"
Assuming that your output only contains
1:2.2.13-12~deb8u3 you should now be fixed, though it will not hurt to explicitly restart:
sudo /etc/init.d/dovecot stop
sudo /etc/init.d/dovecot start