receiving mails works fine.

For a few year thunderbird works fine. Since today I can't send any mail. I got the following message: ErrorMessage: Sending of the message failed. The message could not be sent using Outgoing server (SMTP) securesmtp.t-online.de for an unknown reason. Please verify that your Outgoing server (SMTP) settings are correct and try again.. I check the settings, all fine. I test the settings with Outlook and it works. I use Thunderbird 38.6.0 unter Windows 10 on two computers. Since today both have the same problem. SMTP-Server: securesmpt.t-online.de; Port 465 with SSL/TLS receiving mails works fine.