Zimbra: composing a message ans sending it later

If you are using HIS webmail for sending mail, here is how to do that:

To schedule an email for future delivery in HIS Webmail (Zimbra 10.1): https://webmail.his.com

• Compose your message
• Click the drop-down arrow next to the Send button, and select Send Later.
• Enter your desired date and time, and click OK.

The email will be saved in your Drafts folder until the scheduled time.

Composing a message ans sending it later is a feature from the email app you are using, if you want to do that on another email app: check with the email app documentation to see if they support this feature.