You're probably not sharing the same mailbox location/folder and/or mailbox delivery style (MBOX vs. MDIR) in both Postfix and Dovecot. As a result, Postfix is (correctly) writing under "/home/mailuser/Maildir" (where you see your mail arriving, under the "new" subfolder), but as dovecot is searching somewhere else... it doesn't find such mails (so you get a "no-mail" from it).
As a first check, you should:
- Postfix: check the home_mailbox parameter in /etc/postfix/main.cf:
# The home_mailbox parameter specifies the optional pathname of a
# mailbox file relative to a user's home directory. [...] Specify
# "Maildir/" for qmail-style delivery (the / is required).
home_mailbox = Maildir/
- Dovecot: as suggested by @Kondybas check the mail_location parameter (in CentOS 6.5, at /etc/dovecot/conf.d/10-mail.conf):
# See doc/wiki/Variables.txt for full list. Some examples:
# mail_location = maildir:~/Maildir
# mail_location = mbox:~/mail:INBOX=/var/mail/%u
# mail_location = mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%n
mail_location = maildir:~/Maildir
The two directives above tell Postfix and Dovecot to store incoming mail for "userN", whose home-directory is /home/userN, under the Maildir structure at /home/userN/Maildir
Things are slightly more complex in case of "virtual" users (users not having a proper unix account defined on the machine), in which case both Postfix and Dovecot need to share also the way to get/calculate the home-dir of userN