There are two ways to configure The Bat! email client to play sound on incoming messages: for all messages or for particular messages only, selected by filters.

Play sound for all incoming messages (for POP3 accounts only)

Each POP3 email account has own sound configuration. If you want the email client to play the same sound for all incoming messages, go to the Account Properties dialog. In the Sound section, turn on the checkbox "Play sound when new mail arrives", and choose an audio file to be used as your new mail notification. You can set the time interval during which the mail notification should be played, for example, during working hours only.

Play sound for particular messages

In order to play sound for particular messages, or for IMAP4 accounts, you need to set up filters. From the main menu, select Account -> Sorting Office/Filters. Create a new filter for the incoming mail, add the action "Play a sound" and choose the audio file. You can set the time interval during which the mail notification should be played if you enable the "Enable the sound only within this time interval" option.

Tip: remember to enable the "Continue processing with other filters" option under the Options tab. Move the filter to the first position in the list as the filtering goes top-down.

Using the filters as described above, you can configure custom notification sounds for individual contacts, so The Bat! will play different sounds for different people, based on names or addresses, each time an email arrives from them. You can also set rules to play different sounds based on subject or even based on particular strings in the message body. You can also set up other criteria, e.g. when a sender belongs to a particular group in an address book, or a message has attachments, etc. You can also combine conditions and construct complex criteria. This way, The Bat! will play custom email alert sounds based on your criteria.