MacResponder will ensure that you send an automated away reply from any of your email account.
The application can be configured easily with multiple email accounts as it support both POP3 and SMTP but not IMAP.
You can quickly create an automated response, or even better, set rules for particular messages. This option is easy to use: decide to send or not a message depending on the sender and the subject.
Clicking on the messages tabs will also allow you to created different automated responses which you can use with different rules.
From the application interface itself you'll be able to monitor all the automated responses you've sent and whether to stop or start watching your accounts.
That way you can quickly switch MacResponder on or off. The application itself is shareware but only costs $9. 95, which is not very expensive for an application.
Although it doesn't offer IMAP support, MacResponder is a very useful tool to send automated away responses every time you receive emails in different accounts.