install pigeonhole dovecot
1. Log in to your Roundcube. Usually done going to your mail server. In example mail.yourdomain.com
2. Log in with your username and password. Your username is usually your email address.
3. Go to your Roundcube email settings, like the arrow in the picture below.
4. In the settings column, almost at the bottom, click the Filters. Next, you want to click managesieve in the Filter Sets column. Then in the Filters column, click the + sign to open a new filter rule.
5. Now you filter ruler window should be open. The first thing you need to do is select a name. The name is not important to anyone but you. Just so you recognize what this specific filter rule does. Vrww5gn4 is not a particularly good name. Vacation or out of office would be a better name for this rule.
6. Then you need to select for what incoming emails the rule should apply to. You want to select all messages.
7. Next is execute the following actions. Make sure “Reply with message” is selected. “Message body” is the autoresponder mail itself. That is where you write your message. Message subject is the subject of the mail. Vacation or out of office is good subjects to have here. Reply sender address is the email address you want the recipients to send any replies to. How often send messages(in days), 1 should be enough. Means it send out 1 message to each person who tries to email you.
8. Your Roundcube autoresponder is now finished and click save.