Many Internet mail providers no longer use SMTP-after-POP3 for authentication but expect dedicated SMTP authentication instead.
LANCOM devices with firmware version LCOS 4.00 or later only conduct SMTP authentication if no POP authentication is configured.
Remove the entry for the POP3 server under Log & Trace -> SMTP Options. The LANCOM router now performs an SMTP login as required by the provider.
Any e-mails that accumulated in the mail buffer will be sent after the change. You may receive a number of older e-mails.