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i have latest version of ajenti, and i use ajenti for 6 month, i try mariadb for long time, but you will getting error, and not work probly
if you wann work fine , and every thing be perfect , try mysql-community, and see it with your self

see your nginx logs
and post it here

and check your nginx service is runnig or not
start ajenti service, then open ajenti in your web browser like this, http://your.domain:8000
i made tutorial for installing ajenti on centos 7 
this is the part for installing ajenvi-v-mail

disable se-linux and firewalld 

# yum install ajenti-v-mail 
if you get error
    installing manually exim
    # yum install exim
    # adduser uucp
    # systemctl start exim
    # systemctl enable exim
    installing manually courier
        first install rpm-build
        # yum install rpm-build
        download courier
        # wget
        # wget
            if you get error from above wget , go to, and download manualy 
        install needed package
        # yum install libtool openldap-devel mysql-devel zlib-devel sqlite-devel postgresql-devel gdbm-devel pam-devel expect gcc-c++  perl-Digest-MD5 libtool-ltdl-devel libtool-ltdl libidn-devel fam-devel
        build rpm for courier 
        # rpmbuild -ta courier-unicode-1.1.20150228.tar.bz2
        # cd /root/rpmbuild/RPMS/x86_64
        # rpm -i courier-unicode-1.1.20150228-1.el7.centos.x86_64.rpm
        # rpm -i courier-unicode-debuginfo-1.1.20150228-1.el7.centos.x86_64.rpm
        # rpm -i courier-unicode-devel-1.1.20150228-1.el7.centos.x86_64.rpm
        # cd
        # rpmbuild -ta courier-authlib-0.66.2.tar.bz2
        # cd /root/rpmbuild/RPMS/x86_64
        # rpm -i courier-authlib-0.66.2-1.el7.centos.x86_64.rpm
        # rpm -i courier-authlib-debuginfo-0.66.2-1.el7.centos.x86_64.rpm
        # rpm -i courier-authlib-devel-0.66.2-1.el7.centos.x86_64.rpm
        # rpm -i courier-authlib-ldap-0.66.2-1.el7.centos.x86_64.rpm
        # rpm -i courier-authlib-mysql-0.66.2-1.el7.centos.x86_64.rpm
        # rpm -i courier-authlib-pgsql-0.66.2-1.el7.centos.x86_64.rpm
        # rpm -i courier-authlib-pipe-0.66.2-1.el7.centos.x86_64.rpm
        # rpm -i courier-authlib-sqlite-0.66.2-1.el7.centos.x86_64.rpm
        # rpm -i courier-authlib-userdb-0.66.2-1.el7.centos.x86_64.rpm
        # adduser courier-user
        # passwd courier-user
        # su courier-user
        # cd
        # wget
        # rpmbuild -ta courier-imap-4.16.1.tar.bz2
        # su
        # cd /home/courier-user/rpmbuild/RPMS/x86_64
        # rpm -i courier-imap-4.16.1-2.x86_64.rpm
        # rpm -i courier-imap-debuginfo-4.16.1-2.x86_64.rpm
        # yum install ajenti-v-mail 
        # systemctl start courier-imap 
        # systemctl enable courier-imap 
        # systemctl start courier-authlib 
        # systemctl enable courier-authlib
name server for configure domain name server or any cind of name server like search list or sort list
name server for dns of your network , you shoud set dns your primary ip if you use bind

uninstall mariadb and replace it with mysql-community

its my honor, your welcome

you should try Custom routers on mail section >> advanced tab
just use this for custom routers
debug_print = "R: catch_all for $local_part@$domain" 
driver = redirect 
domains = 
data =
please explain more about how your ajenti stop working, what cind of error you get?
i dont know which os do you use, or do you have firewall or iptables,
but i using centos 7 and firewalld, fallow these commands solved my problem
firewall-cmd --permanent --add-service=http
firewall-cmd --permanent --add-service=https
firewall-cmd --permanent --zone=public --add-port=443/tcp 
firewall-cmd --reload
i realy wann help,i try hard, but i dont know any idea , so sorry
but i think you shoud use ajenti behind nginx