Hurray, I'm able to send mail! I forgot to give the iPad credentials for smtp *facepalm* My Mistake, sorry...
But, I'm still not able to receive Mail
EDIT:
Found some entries in the log,
Oct 26 18:12:44 fuwu-logistics dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=95.116.170.12, lip=194.55.15.31, session=<cZ1midKVcuRfdKoM>
Oct 26 18:12:44 fuwu-logistics dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=95.116.170.12, lip=194.55.15.31, session=<e09oidKVdORfdKoM>
Oct 26 18:12:47 fuwu-logistics dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=95.116.170.12, lip=194.55.15.31, session=<+2aVidKVduRfdKoM>
Oct 26 18:12:48 fuwu-logistics dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=95.116.170.12, lip=194.55.15.31, session=<SyOjidKVeORfdKoM>
Oct 26 18:12:50 fuwu-logistics dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=95.116.170.12, lip=194.55.15.31, session=<Tqu8idKVeeRfdKoM>
Oct 26 18:12:50 fuwu-logistics dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=95.116.170.12, lip=194.55.15.31, session=<zaS9idKVeuRfdKoM>
Oct 26 18:12:50 fuwu-logistics dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=95.116.170.12, lip=194.55.15.31, session=<jqLAidKVe+RfdKoM>
Oct 26 18:12:50 fuwu-logistics dovecot: imap-login: Aborted login (no auth attempts in 0 secs): user=<>, rip=95.116.170.12, lip=194.55.15.31, session=<T97BidKVfORfdKoM>
But I specified a user this time...