Here is a quick patch to support doveadm pw + DIGEST_MD5 passwords works with dovecot + postfix.

diff -d postfixadmin-2.3.5/config.inc.php /var/www/html/postfix/config.inc.php
99c100
< $CONF['encrypt'] = 'md5crypt';
---
> $CONF['encrypt'] = 'dovecot:DIGEST-MD5';
109c110
< $CONF['dovecotpw'] = "/usr/sbin/dovecotpw";
---
> $CONF['dovecotpw'] = "/usr/bin/doveadm pw";
diff -d postfixadmin-2.3.5/create-mailbox.php /var/www/html/postfix/create-mailbox.php
160c160
<         $password = pacrypt ($fPassword);
---
>         $password = pacrypt ($fPassword,"",$fUsername.'@'.$fDomain);
diff -d postfixadmin-2.3.5/edit-admin.php /var/www/html/postfix/edit-admin.php
80c80
<                     $fPassword = pacrypt($fPassword);
---
>                     $fPassword = pacrypt($fPassword,"",$username);
diff -d postfixadmin-2.3.5/edit-mailbox.php /var/www/html/postfix/edit-mailbox.php
110c110
<             $formvars['password'] = pacrypt($fPassword);
---
>             $formvars['password'] = pacrypt($fPassword,"",$fUsername);
diff -d postfixadmin-2.3.5/functions.inc.php /var/www/html/postfix/functions.inc.php
1149c1149
< function pacrypt ($pw, $pw_db="")
---
> function pacrypt ($pw, $pw_db="", $username="")
1241,1242c1241
<
<         $pipe = proc_open("$dovecotpw '-s' $method", $spec, $pipes);
---
>         $pipe = proc_open("$dovecotpw '-s' $method '-u' $username", $spec, $pipes);
1267c1266,1267
<             $password = trim(str_replace('{' . $method . '}', '', $password));
>             $password = trim($password);
2341c2341
<         $password = pacrypt($fPassword);
---
>         $password = pacrypt($fPassword,"",$fUsername);
diff -d postfixadmin-2.3.5/login.php /var/www/html/postfix/login.php
61c61
<         $password = pacrypt ($fPassword, $row['password']);
---
>         $password = pacrypt ($fPassword, $row['password'],$fUsername);
diff -d postfixadmin-2.3.5/password.php /var/www/html/postfix/password.php
56c56
<         $checked_password = pacrypt ($fPassword_current, $row['password']);
---
>         $checked_password = pacrypt ($fPassword_current, $row['password'], $username);
79c79
<         $password = pacrypt ($fPassword);
---
>         $password = pacrypt ($fPassword,"",$username);