I need some help with my Dovecot and Postfix configs - I'm unable to log in on my mail server

[Nils]

Hello,

currently I'm working on my first mailserver but I can't log in to the 
account I made. For now my client (Mozlla Thunderbird) detects the 
server config (STARTTLS, Port, ...) but it is "Unable to log in at 
server. Probbly wrong configuration, username or passsword".

I know that I added username and password correctly so there must 
something else be wrong.

I run Debian 10 x64 on a fresh installation.
Installed are: postfix, postfix-pcre, dovecot-core, dovecot-imapd and 
dovecot-pop3d.
Dovecot is version 2.3.4.1, Postfix is 3.4.10.

Here are my configurations:
Postfix main.cf: https://pastebin.com/S17jWDQd
Postfix master.cf: https://pastebin.com/W0nynZG6
dovecot.conf: https://pastebin.com/tMD90Znn

This is what my server logs (mail.info, mail.warn) tell me:
root at bgrsld-mail0:~# tail /var/log/mail.info
Jul 17 18:22:08 bgrsld-mail0 postfix/submission/smtpd[8472]: improper 
command pipelining after EHLO from unknown[192.168.2.110]: QUIT\r\n
Jul 17 18:22:08 bgrsld-mail0 postfix/submission/smtpd[8465]: disconnect 
from unknown[192.168.2.110] ehlo=1 quit=1 commands=2
Jul 17 18:22:08 bgrsld-mail0 postfix/submission/smtpd[8472]: disconnect 
from unknown[192.168.2.110] ehlo=1 quit=1 commands=2
Jul 17 18:24:59 bgrsld-mail0 postfix/submission/smtpd[8485]: warning: 
dict_nis_init: NIS domain name not set - NIS lookups disabled
Jul 17 18:24:59 bgrsld-mail0 postfix/submission/smtpd[8485]: connect 
from unknown[192.168.2.110]
Jul 17 18:24:59 bgrsld-mail0 postfix/submission/smtpd[8485]: improper 
command pipelining after EHLO from unknown[192.168.2.110]: QUIT\r\n
Jul 17 18:24:59 bgrsld-mail0 postfix/submission/smtpd[8485]: disconnect 
from unknown[192.168.2.110] ehlo=1 quit=1 commands=2
Jul 17 18:28:19 bgrsld-mail0 postfix/anvil[8473]: statistics: max 
connection rate 2/60s for (submission:192.168.2.110) at Jul 17 18:22:08
Jul 17 18:28:19 bgrsld-mail0 postfix/anvil[8473]: statistics: max 
connection count 2 for (submission:192.168.2.110) at Jul 17 18:22:08
Jul 17 18:28:19 bgrsld-mail0 postfix/anvil[8473]: statistics: max cache 
size 1 at Jul 17 18:22:08
root at bgrsld-mail0:~# tail /var/log/mail.warn
Jul 17 18:21:50 bgrsld-mail0 postfix/postfix-script[8290]: warning: 
symlink leaves directory: /etc/postfix/./makedefs.out
Jul 17 18:22:08 bgrsld-mail0 postfix/submission/smtpd[8465]: warning: 
dict_nis_init: NIS domain name not set - NIS lookups disabled
Jul 17 18:22:08 bgrsld-mail0 postfix/submission/smtpd[8472]: warning: 
dict_nis_init: NIS domain name not set - NIS lookups disabled
Jul 17 18:24:59 bgrsld-mail0 postfix/submission/smtpd[8485]: warning: 
dict_nis_init: NIS domain name not set - NIS lookups disabled

(I removed any information from older issues that are already solved, 
thats why mail.warn misses a few lines and there is no mail.err, 
mail.err hadn't any newer messages)

Here is my only line from dovecot's userpass file (/maildata/userpass):

nils at intern.xxx.xxx:{CRYPT}$2y$05$kkxElxFGsLSyTJwbEaPZzO/QA33vGY3oGyHcgEZa9rpklgBTKQw9O

My postfix vhosts file (/maildir/vhosts)

intern.xxx.xxx

My postfix vmaps file (/maildir/vmaps)

nils at intern.xxx.xxx intern.xxx.xxx/nils/

I've also created the hased database with 'postmap /maildata/vmaps'

This is the script I've used to create my user database: 
https://pastebin.com/9uViNqjB

I haven't worked with postfiy or dovecot yet so there are many things I 
don't know. Because of this a lot of my configurations is copied from an 
iRedMail installation. I know that taking these configs may cause some 
problems but I don't know where to change them or what else is wrong or 
missing.

Thank you for any help!
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