eM Client doesn't sync with one specific t-online-account

I’ve recently installed eM Client for several users who are using different t-online-accounts.

One of these accounts always failes to sync with the IMAP-Server. User name and password are correct, host (secureimap.t-online.de) and port (993) are correct, too. Yet it doesn’t work.

What’s wrong?

I would check to see if the host allows unsecured applications to work with there server.  example gmail will not work with outlook / em client  / Thunderbird to name a few.  also make sure that the IMAP options  are c heck on the host server.

Thanks for your reply - the problem with this account was that sometimes it worked, but most of the time it didn’t.  Right now it works - always. I didn’t change anything (well, I’ve activated and de-activated “Download messanges for offline-use”, but what effect could this have…?)