A user with a Microsoft Exchange server mailbox wanted to prepare some messages to send later but didn't want to leave Outlook open or open it to send.
I want to schedule an email to send on the Exchange Server so that I can schedule emails to send while I’m on vacation without having to boot my laptop and open my email 1-2 times per day. I know how to do this in desktop Outlook, but you need to open Outlook on your laptop for this to work. Can I do this using Outlook on the web?
Deferred delivery is not supported in Outlook on the web. You can delay sending mail for a few seconds (to prevent accidental sends) but cannot configure a message to send later, as you can in Outlook on Windows.
Because you are using a Microsoft Exchange mailbox (either on-prem or Office 365 Exchange online) you can send messages later, with Outlook closed, as long as you can set up the account in Outlook desktop using Online mode.
When you use online mode, the deferred messages are submitted to the Exchange message queue and held until the scheduled time. (Outlook doesn’t have a local cache when you use online mode, so it can’t hold them at the client.)
This only works if you have the account set up in Outlook in online mode. It will not work with Outlook.com accounts as they do not support online mode.
By default, Outlook sets Exchange accounts up in cached mode. You can check in File, Account Settings: open the account settings dialog, and double click on the account. Cached will be ticked by default when you set up the account, untick it to drop to online mode. The status bar should say 'Online', when you have cached mode turned off.
Before you disable cached mode: if you have the messages already in the Outbox move them to Drafts folder first so they will sync to the server. After you switch to online mode, go to the Drafts folder and Send the messages.
You won't see the messages if you look in Outlook on the web, so you just have to trust Exchange. To verify it is working, create an email to email address you can check on your phone. Defer it for 15 min from now and click Send. Close Outlook. If you receive the message in 15 min, it’s set up properly.
If you don't use Outlook for Windows or can't use Online mode, you can vote for (and comment on) this suggestion at Outlook uservoice: Ability to Schedule/Delay Sending Emails 365 ONWEB