Hier die logs der verschiedenen Versuche mit unterschiedlicher Auth.
02.06.2016, 17:44:55: SEND - sending mail message(s) - 1 message(s) in queue
02.06.2016, 17:44:55: SEND - Connecting to SMTP server smtp.1und1.de on port 587
02.06.2016, 17:44:55: SEND - Initiating TLS handshake
>02.06.2016, 17:44:55: SEND - Certificate S/N: D2B700CA910A9B48806C39B55A0C93FF, algorithm: RSA (2048 bits), issued from 1/29/2014 10:01:50 AM to 2/3/2017 11:59:59 PM, for 1 host(s): smtp.1und1.de.
>02.06.2016, 17:44:55: SEND - Owner: DE, 1 und 1 Internet AG, Rheinland-Pfalz, Montabaur, server-certs@1und1.de, smtp.1und1.de.
>02.06.2016, 17:44:55: SEND - Root: generated by avast! antivirus for SSL/TLS scanning, avast! Web/Mail Shield, avast! Web/Mail Shield Root
02.06.2016, 17:44:55: SEND - TLS handshake complete
02.06.2016, 17:44:55: SEND - connected to SMTP server
02.06.2016, 17:44:55: SEND - authenticating (plain)...
02.06.2016, 17:45:15: SEND - Server reports error. The response is:
02.06.2016, 17:45:15: SEND - authenticating (login)...
02.06.2016, 17:45:15: SEND - Server reports error. The response is:
02.06.2016, 17:45:15: SEND - connection finished - 0 message(s) sent
02.06.2016, 17:45:15: SEND - Some messages were not sent - check the log for details
02.06.2016, 17:45:29: SEND - sending mail message(s) - 1 message(s) in queue
02.06.2016, 17:45:29: SEND - Connecting to SMTP server smtp.1und1.de on port 587
02.06.2016, 17:45:29: SEND - Initiating TLS handshake
>02.06.2016, 17:45:29: SEND - Certificate S/N: D2B700CA910A9B48806C39B55A0C93FF, algorithm: RSA (2048 bits), issued from 1/29/2014 10:01:50 AM to 2/3/2017 11:59:59 PM, for 1 host(s): smtp.1und1.de.
>02.06.2016, 17:45:29: SEND - Owner: DE, 1 und 1 Internet AG, Rheinland-Pfalz, Montabaur, server-certs@1und1.de, smtp.1und1.de.
>02.06.2016, 17:45:29: SEND - Root: generated by avast! antivirus for SSL/TLS scanning, avast! Web/Mail Shield, avast! Web/Mail Shield Root
02.06.2016, 17:45:29: SEND - TLS handshake complete
02.06.2016, 17:45:29: SEND - connected to SMTP server
02.06.2016, 17:45:29: SEND - authenticating (plain)...
02.06.2016, 17:45:48: FETCH - receiving mail messages
02.06.2016, 17:45:48: FETCH - Connecting to POP3 server pop.gmx.net on port 995
02.06.2016, 17:45:48: SEND - sending mail message(s) - 2 message(s) in queue
02.06.2016, 17:45:48: SEND - Connecting to SMTP server smtp.1und1.de on port 587
02.06.2016, 17:45:48: FETCH - Initiating TLS handshake
02.06.2016, 17:45:48: SEND - Initiating TLS handshake
>02.06.2016, 17:45:48: FETCH - Certificate S/N: 9630829EC5C64948BDF8CF21FB54E569, algorithm: RSA (2048 bits), issued from 11/12/2013 10:19:29 AM to 11/17/2016 11:59:59 PM, for 2 host(s): pop.gmx.net, pop.gmx.de.
>02.06.2016, 17:45:48: FETCH - Owner: DE, 1&1 Mail & Media GmbH, Rhineland-Palatinate, Montabaur, server-certs@1und1.de, pop.gmx.net.
>02.06.2016, 17:45:48: FETCH - Root: generated by avast! antivirus for SSL/TLS scanning, avast! Web/Mail Shield, avast! Web/Mail Shield Root
02.06.2016, 17:45:48: FETCH - TLS handshake complete
>02.06.2016, 17:45:48: SEND - Certificate S/N: D2B700CA910A9B48806C39B55A0C93FF, algorithm: RSA (2048 bits), issued from 1/29/2014 10:01:50 AM to 2/3/2017 11:59:59 PM, for 1 host(s): smtp.1und1.de.
>02.06.2016, 17:45:48: SEND - Owner: DE, 1 und 1 Internet AG, Rheinland-Pfalz, Montabaur, server-certs@1und1.de, smtp.1und1.de.
>02.06.2016, 17:45:48: SEND - Root: generated by avast! antivirus for SSL/TLS scanning, avast! Web/Mail Shield, avast! Web/Mail Shield Root
02.06.2016, 17:45:48: SEND - TLS handshake complete
02.06.2016, 17:45:48: SEND - connected to SMTP server
02.06.2016, 17:45:48: SEND - authenticating (plain)...
02.06.2016, 17:45:49: FETCH - connected to POP3 server
!02.06.2016, 17:45:49: FETCH - Server reports error. The response is: -ERR authentication failed
02.06.2016, 17:45:49: SEND - Server reports error. The response is:
02.06.2016, 17:45:49: SEND - authenticating (login)...
02.06.2016, 17:45:49: SEND - Server reports error. The response is:
02.06.2016, 17:45:49: SEND - connection finished - 0 message(s) sent
02.06.2016, 17:45:49: SEND - Some messages were not sent - check the log for details
02.06.2016, 17:45:57: SEND - sending mail message(s) - 1 message(s) in queue
02.06.2016, 17:45:57: SEND - Connecting to SMTP server smtp.1und1.de on port 587
02.06.2016, 17:45:57: SEND - Initiating TLS handshake
>02.06.2016, 17:45:57: SEND - Certificate S/N: D2B700CA910A9B48806C39B55A0C93FF, algorithm: RSA (2048 bits), issued from 1/29/2014 10:01:50 AM to 2/3/2017 11:59:59 PM, for 1 host(s): smtp.1und1.de.
>02.06.2016, 17:45:57: SEND - Owner: DE, 1 und 1 Internet AG, Rheinland-Pfalz, Montabaur, server-certs@1und1.de, smtp.1und1.de.
>02.06.2016, 17:45:57: SEND - Root: generated by avast! antivirus for SSL/TLS scanning, avast! Web/Mail Shield, avast! Web/Mail Shield Root
02.06.2016, 17:45:57: SEND - TLS handshake complete
02.06.2016, 17:45:57: SEND - connected to SMTP server
02.06.2016, 17:45:57: SEND - authenticating (plain)...
02.06.2016, 17:46:08: SEND - Server reports error. The response is:
02.06.2016, 17:46:08: SEND - authenticating (login)...
02.06.2016, 17:46:08: SEND - Server reports error. The response is:
02.06.2016, 17:46:08: SEND - connection finished - 0 message(s) sent
02.06.2016, 17:46:08: SEND - Some messages were not sent - check the log for details
02.06.2016, 17:46:17: SEND - Server reports error. The response is:
02.06.2016, 17:46:17: SEND - authenticating (login)...
02.06.2016, 17:46:17: SEND - Server reports error. The response is:
02.06.2016, 17:46:17: SEND - connection finished - 0 message(s) sent
02.06.2016, 17:46:17: SEND - Some messages were not sent - check the log for details
02.06.2016, 17:46:51: SEND - sending mail message(s) - 1 message(s) in queue
02.06.2016, 17:46:51: SEND - Connecting to SMTP server smtp.1und1.de on port 587
02.06.2016, 17:46:51: SEND - Initiating TLS handshake
>02.06.2016, 17:46:51: SEND - Certificate S/N: D2B700CA910A9B48806C39B55A0C93FF, algorithm: RSA (2048 bits), issued from 1/29/2014 10:01:50 AM to 2/3/2017 11:59:59 PM, for 1 host(s): smtp.1und1.de.
>02.06.2016, 17:46:51: SEND - Owner: DE, 1 und 1 Internet AG, Rheinland-Pfalz, Montabaur, server-certs@1und1.de, smtp.1und1.de.
>02.06.2016, 17:46:51: SEND - Root: generated by avast! antivirus for SSL/TLS scanning, avast! Web/Mail Shield, avast! Web/Mail Shield Root
02.06.2016, 17:46:51: SEND - TLS handshake complete
02.06.2016, 17:46:51: SEND - connected to SMTP server
02.06.2016, 17:46:51: SEND - authenticating (plain)...
02.06.2016, 17:47:11: SEND - Server reports error. The response is:
02.06.2016, 17:47:11: SEND - authenticating (login)...
02.06.2016, 17:47:11: SEND - Server reports error. The response is:
02.06.2016, 17:47:11: SEND - connection finished - 0 message(s) sent
02.06.2016, 17:47:11: SEND - Some messages were not sent - check the log for details
02.06.2016, 17:50:49: FETCH - receiving mail messages
02.06.2016, 17:50:49: FETCH - Connecting to POP3 server pop.gmx.net on port 995
02.06.2016, 17:50:49: FETCH - Initiating TLS handshake
02.06.2016, 17:50:49: SEND - sending mail message(s) - 2 message(s) in queue
02.06.2016, 17:50:49: SEND - Connecting to SMTP server smtp.1und1.de on port 587
>02.06.2016, 17:50:49: FETCH - Certificate S/N: 9630829EC5C64948BDF8CF21FB54E569, algorithm: RSA (2048 bits), issued from 11/12/2013 10:19:29 AM to 11/17/2016 11:59:59 PM, for 2 host(s): pop.gmx.net, pop.gmx.de.
>02.06.2016, 17:50:49: FETCH - Owner: DE, 1&1 Mail & Media GmbH, Rhineland-Palatinate, Montabaur, server-certs@1und1.de, pop.gmx.net.
>02.06.2016, 17:50:49: FETCH - Root: generated by avast! antivirus for SSL/TLS scanning, avast! Web/Mail Shield, avast! Web/Mail Shield Root
02.06.2016, 17:50:49: SEND - Initiating TLS handshake
02.06.2016, 17:50:49: FETCH - TLS handshake complete
>02.06.2016, 17:50:49: SEND - Certificate S/N: D2B700CA910A9B48806C39B55A0C93FF, algorithm: RSA (2048 bits), issued from 1/29/2014 10:01:50 AM to 2/3/2017 11:59:59 PM, for 1 host(s): smtp.1und1.de.
>02.06.2016, 17:50:49: SEND - Owner: DE, 1 und 1 Internet AG, Rheinland-Pfalz, Montabaur, server-certs@1und1.de, smtp.1und1.de.
>02.06.2016, 17:50:49: SEND - Root: generated by avast! antivirus for SSL/TLS scanning, avast! Web/Mail Shield, avast! Web/Mail Shield Root
02.06.2016, 17:50:49: SEND - TLS handshake complete
02.06.2016, 17:50:49: SEND - connected to SMTP server
02.06.2016, 17:50:49: SEND - authenticating (plain)...
02.06.2016, 17:50:49: FETCH - connected to POP3 server
!02.06.2016, 17:50:49: FETCH - NTLM/MSN authentication is not supported by the server
02.06.2016, 17:50:49: FETCH - connection finished - 0 messages received
02.06.2016, 17:51:09: SEND - Server reports error. The response is:
02.06.2016, 17:51:09: SEND - authenticating (login)...
02.06.2016, 17:51:09: SEND - Server reports error. The response is:
02.06.2016, 17:51:09: SEND - connection finished - 0 message(s) sent
02.06.2016, 17:51:09: SEND - Some messages were not sent - check the log for details