I used this script around 2015 I guess to manage easily the email accounts, just to archive it I paste it here, I dont know if it works or not

mailadm.sh

#!/bin/bash
#MailAdm - Manage you mailboxes easily

#Checking for Root Account
if [[ $EUID -ne 0 ]]; then
	  echo "Script can be executed only by root"
	  exit 1
fi

add_user() {
	if [[ -z $user ]];then
		echo "Missing Username"
		exit 1
	fi
	check_user=$(cut -f 1 -d : /etc/passwd | grep "^$user$" )
	if [ ! -z "$check_user" ]; then
		echo "User \"$user\" Exists"
		exit 1
	fi
	useradd $user -s $shell -m
	mkdir /home/$user/conf /home/$user/mail
	mkdir /home/$user/conf/keys
	chmod 751 /home/$user/mail
	chmod 755 /home/$user/conf
	chmod a+x /home/$user
}

dkim_keys() {
	cd /home/$user/conf/keys
	openssl genrsa -out $user.pem 1024
	openssl rsa -pubout -in $user.pem -out $username.pub
}

set_dns() {
	p=$(cat /home/$user/conf/keys/$user.pub | grep -v ' KEY---'|tr -d '\n')
	echo "
		Please Create Following Records in DNS server
		1) _dmarc IN TXT \"v=DMARC1; p=none\"
		2) @ IN TXT \"v=spf1 a mx ip4:$IP ?all\"
		3) _domainkey IN TXT \"t=y; o=~;\"
		4) mail._domainkey IN TXT \"v=DKIM1; k=rsa; p=$p\"
		5) mail IN A $IP
		6) smtp IN A $IP
		7) imap IN A $IP
		8) pop IN A $IP
		9) @ IN MX 10 mail.$domain
	"
}

prep_domain() {
	mkdir /home/$user/conf/$domain
	mkdir /home/$user/mail/$domain
	touch /home/$user/conf/$domain/{aliases,passwd,fwd_only}
	ln -s /home/$user/conf/$domain /etc/exim4/domains/$domain
	cp /home/$user/conf/keys/$user.pem /home/$user/conf/$domain/dkim.pem
	chmod 771 /home/$user/conf/$domain
	chmod 660 /home/$user/conf/$domain/*
	chmod 771 /etc/exim4/domains/$domain
	chmod 770 /home/$user/mail/$domain
	chown -R Debian-exim:mail /home/$user/conf/$domain
	chown -R dovecot:mail /home/$user/conf/$domain/passwd
	chown $user:mail /home/$user/mail/$domain
}

add_account() {
	salt=$(</dev/urandom tr -dc A-Za-z0-9 | head -c10)
	read -p "Please Enter your password: " password
	md5="{MD5}$(perl -e 'print crypt('$password', '$salt'),"\n"')"
	str="$account:$md5:$user:mail::/home/$user:0"
	echo $str >> /home/$user/conf/$domain/passwd

}

add_mail_domain() {
	if [ "$#" != 3 ]; then
		error "Usage : ssc $1 USER DOMAIN"
	fi
	user=$2
	domain=$3
	add_user
	dkim_keys
	prep_domain
	set_dns
}

add_mail_account() {
	if [ "$#" != 4 ]; then
		error "Usage : ssc $1 USER DOMAIN ACCOUNT"
	fi
	user=$2
	domain=$3
	account=$4
	add_account
}

action=$1
case $action in
	domain)
		add_mail_domain $@
	;;
	account)
		add_mail_account $@
	;;
	*)
		echo "mailadm domain USER DOMAIN"
		echo "mailadm account USER DOMAIN ACCOUNT"
		exit 1
	;;
esac