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https://www.thunderbird-mail.de/forum/thread/47327-login-to-server-imap-1und1-de-failed/
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https://www.ionos.de/hilfe/e-mail-office/basic-mail-verwalten/einstellungen-fuer-ihr-e-mail-programm-imap-pop3/
https://support.mozilla.org/questions/1052629
https://support.mozilla.org/questions/1066957
https://github.com/imapsync/imapsync/issues/140
https://www.giga.de/downloads/internet/email/email-server-imap-pop3-einstellungen-fuer-web.de-gmx-gmail-co/
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https://www.batboard.net/index.php/Thread/10341-1und1-mailkonto-abrufen-ergibt-Authentifikationsfehler/
https://www.jam-software.de/knowledgebase/smartpop2exchange/index4.shtml
https://discussions.apple.com/thread/4103977
https://web.nettworks.org/forum/index.php?t=msg&goto=30496&