A message that is deleted in Gmail will be sent to your trash, where it will be automatically permanently deleted after 30 days (or if you empty the trash manually). Messages deleted from the trash, whether manually or automatically after 30 days, can NOT be recovered!
Why would you delete?
- You are certain you will never need to refer to it again
- It contains confidential information you should not have been sent
- It has a large attachment you no longer need
A message that is archived in Gmail will be removed from your inbox, but will still appear in searches, in All Mail, and in any labels you assigned to it. Note that this is different from Outlook's use of the word "Archive". In Google, archived mail is not downloaded to your computer, just taken out of your Inbox. It still counts against your mail quota.
Why would you archive?
- You may want to refer to the message in the future, but do not want it to appear in your Inbox
- You try to maintain "Inbox Zero" and/or use your inbox as a to-do list of active emails