My boss uses Outlook for his work email. He has an IMAP gmail apps-based business email account.  All of his Outlook folders are synced with gmail.

His Outlook .pst file is now 18Gb.  If I archive some older emails in Outlook, will it mess up the IMAP folders that he is syncing with on the gmail servers?

Thanks!

Which version of Outlook are we talking about here?
What is the size of his mailbox as reported by the Gmail web interface?

He can unsubscribe from folders he is not actively using anymore.
You can also archive to a pst-file but that will take it off the server and store it on his local computer only.

Additionally see: Gmail accounts and disproportionally large pst-files

He is using Outlook 2010.  Gmail reports the total mailbox size on the server as 7Gb.  When I look at the associated .pst file, it's 18Gb. So there might be a lot of old mail in that .pst file that he accumulated before he switched to Gmail as his mail service. And he is unsubscribed from the Gmail All Mail folder.  But I don't think his .pst file has ever been compacted, so I will do that.

He is using all the folders and doesn't want me to unsubscribe from any of them.  (He is adamant that he has to go back through his old emails occasionally.)

So if he doesn't want to lose the emails on the server, he should not archive them locally, correct?

It sounds like he should to go through his Gmail account and put the older emails under a separate label, and then unsubscribe from that folder. Will that work? Or is this overkill, because all the emails will still be on the Gmail server in the All Mail folder/label?

Thanks so much!