For Outlook software, the term ‘Archive’ means different things depending on the version of Outlook you’re using and the type of mailbox you’re connected to.
Archive is a way to move messages from your regular folders to a separate location that’s ‘out of sight’. It’s a middle ground between keeping messages and deleting them completely.
In organizations, Archive reduces the clutter of main folders like Inbox but keeps the messages to comply with in-house or legal document retention rules. Individuals use Archive to keep their Inbox down to size by moving aside secondary or older messages.
The reason for Archive and how it works has changed over time.
A history of Archiving
The original Archive feature moved messages from the main data file to a separate Outlook data file (PST).
It was Microsoft’s workaround to complaints about Outlook running slowly. In those days (slower computers, less memory) Outlook became sluggish as the mailbox got bigger. Microsoft’s response was to make the mailbox smaller by encouraging customers to use Archive and a second mail store.
It’s a bit like a car maker telling drivers to improve gas mileage by putting less people and stuff in the vehicle. Sure, the car uses less fuel but it you have to leave your kids and luggage at home.
AutoArchive prompts appeared to Outlook users, encouraging the use of Archive.
Archive as a separate data store solved Microsoft’s sales and support problem but made life harder for customers. The AutoArchive prompts where there to solve Microsoft’s support problem.
The separate Archive PST had to be searched separately, which many people forgot to do. The second data file was overlooked when moving or backing up computers, leading to data loss. Microsoft now admits the shortcomings of AutoArchive but downplayed them for many years.
Over time, the need for Outlook’s AutoArchive workaround reduced. Computers got faster, especially hard drives and memory. Outlook became more efficient and could cope with much larger data files (PST were limited to less than 2GB, now there’s no practical size limit). Searching is now possible via the server for Exchange Server users.
For these reasons, Office-Watch.com recommended against using Archive or AutoArchive.
Archive isn’t really necessary. AutoArchive is a workaround for a problem that doesn’t exist or is much reduced now.
Outlook 365 and Outlook 2019
Outlook 365 and 2019 for Windows has an ‘Archive’ button but it’s a very different thing from past Outlook’s see Archive in Outlook 365 and Outlook 2016/2019 for Windows
AutoArchive still exists in Outlook 365/2019 but there doesn’t seem to be the prompt to use it and the options are hidden.