POP goes the email: migrate to IMAP

Some of us are old enough to remember using pine and other Unix screen-based email readers. Younger folks might have cut their teeth on Eudora and other Mac apps (back when we called them “software programs”) that could seamlessly log into a mail server, retrieve email locally, and let us interact with it. The first widely successful protocol of that type was Post Office Protocol (POP).1

POP’s job was to download mail. If you left it on the server, it was just a giant mailbox. However, it was all we had, and we liked it!2

POP is now over 40 years old and has been effectively superseded by IMAP (Internet Message Access Protocol) for decades. The easiest comparison between the two is that POP is like a huge stack of printed messages, while IMAP is a desk organizer with labels in which paper has been sorted for easy retrieval.3

Simulated appearance of POP email organization. Photo by Alexander Grey on Unsplash

However, because many of us started with POP, we wound up just continuing to use it. (I only switched to IMAP in the late 2010s.) Six Color reader Neil writes is one of those people. He writes:

I have over 20 years of email, and several accounts, on my Mac, all housed in Apple’s Mail.app, categorized in several dozen folders (but my “All Inboxes” has grown to almost 10,000 emails – sigh).…it didn’t matter because I didn’t have a second email client reading the same emails.

However, because he now reads email on multiple devices, he’s found POP frustrating. He wants to migrate to IMAP, but his host doesn’t offer a migration path while retaining the same mailbox. He has to delete his old POP mailbox and create a new IMAP account. Of course, he doesn’t want to lose any of the email archive that he’s left stowed online in the POP account.

My hunch is that it is doable (maybe even straightforward), but I’m afraid to just try it for fear of losing some or all of my archives.

I can bring good tidings: there’s no technical issue with migrating your email from POP to IMAP, and you won’t lose anything if you take care. The less-good news: it requires some methodical work and a bit of patience.

Why POP stuck around so long

POP’s appeal was always its simplicity. Your email client downloaded messages from the server with an option to delete them afterward (or after a set period). Because of storage limits, you could typically keep a relatively small number of messages on the server, and regularly had to move everything else to local storage on your Mac. The server was mostly a temporary repository.

This worked well in a mostly single-device era, or when we had a desktop computer in one location and a laptop in the other. I developed a habit of using POP to read email on my laptop by having the email app on that computer download messages without deleting them. I would then download and delete the messages on my desktop computer and sort them into folders.4 That kept my mailbox from getting too huge, but I could read email away from my desktop.

Once you had multiple devices on which you wanted to read email, everything went out the window for POP. IMAP’s first version appeared not that long after POP’s initial release, but it took many more years for companies offering mail services to adopt IMAP. This was almost certainly because mail hosts had constrained storage space—as did we all—and pushed their users to download mail, something POP was well-suited for. As storage costs plummeted and people wanted more access to the same email in different locations, IMAP’s higher computational and storage needs made financial sense. (Or, with Google and Gmail, competitive sense.)

IMAP treats the server as the source of “truth.” Your mail client shows you what’s on the server, and actions you take—reading, deleting, filing into folders—sync back. Multiple devices see the same state. I have more gigabytes of storage than I need on most of my email hosts, so I can leave email there indefinitely. (Leaving your mail on solely on a server comes with huge risks! I’ll write about that sometime.)

The slight catch for longtime POP users is, of course, that all that mail you’ve accumulated over the years is likely just on your Mac, not on a server. You may need to do a few kinds of copying.

Download all those messages as a new archive

Having 10,000 messages on a server, whether POP or IMAP, personally makes me nervous. I’m not sure if Neil—or you, dear reader—has made a local copy of those emails, but his note indicates he’s filed some into folders, which indicates local storage.

The only way to ensure you have retrieved every message locally from a POP email server before deleting them is to perform a clean download. If you set up another account for the same mail host in Mail in your regular macOS account, I’m concerned about the conflicts that could result.

Instead, I suggested setting up a new macOS account, which can be temporary, for the most likely successful outcome. Here’s how:

Mail’s POP account settings let you choose to leave messages on the server or delete them after retrieval.

Create a new macOS account, then log into it.

Launch Mail and follow prompts to duplicate your email account set up for POP in that account.

Set the download option to keep messages, not delete them, after retrieval.

Choose Mailbox: New Mailbox, and then choose On My Mac, and name the mailbox something identifiable, like downloaded POP email.

You can’t drag the Inbox folder to the On My Mac section, but you can click the POP Inbox folder, choose Edit: Select All, then drag the file selection on top of the new On My Mac folder you just created.

After the messages have downloaded, you can create an archive that you can import later if you need to:

Apple Mail lets you import messages in the standard mailbox format.

Control/right-click the mailbox under On My Mac.

Choose Export Mailbox.

Select a location to save the mailbox that you can access from your main account.

Log out of this account and log back into your main macOS account. Mail exports it as a standard mbox file that can be imported into Mail or any modern email app.

In the Mail app, you can choose the exported mbox file into Mail by choosing File: Import Mailboxes, selecting “Files in mbox format,” clicking Continue, selecting the file, and completing the remaining steps.

After you’ve imported those messages, you can delete the new macOS account if you don’t think you’ll need it again. (I like to keep a secondary login for Mac tasks that work best outside my primary account.)

The migration strategy

You should see On My Mac with one or more folders if any email is stored locally.

In Neil’s case, there’s a split between locally stored email, which appears in the Mail app under the On My Mac section of the Mail sidebar, and email stored on a server, such as Apple’s iCloud or another mail host.

If you don’t see an On My Mac section, then you don’t have mail stored locally. If you haven’t followed the steps in the previous section, you should return to it and download all your messages via POP, then copy them locally.

As always, start with a backup. Make sure your Mac is backed up (always good advice), and then, in particular, that the Mail folder at ~/Library/Mail is completely up to date. If you’re using a different email app, make sure you know where it keeps its local mail store, and back that up.

Now you can proceed:

Delete all the messages from your POP mailbox on the mail host. It may be much faster to log into the host’s Webmail interface and delete the messages. Be sure you don’t delete your account, just the messages or POP mailbox.

At this stage, you may be required to delete the Mail account entry for the POP mailbox: select it in the Accounts sidebar, click the minus icon, and then confirm its removal.

Now you can use the mail host’s procedure for creating an IMAP account.

Once configured, go to Mail: Settings: Accounts, click the plus + icon at the lower-left corner, and follow the steps to add the IMAP account.5

With the account set up, you can use the Webmail interface or the Mail app to create folders on the server.

If you want to copy mail back to the server to have access to it while not at your Mac, you can go to the folder under On My Mac, select some or all of the contents, and drag those items to the appropriate folder in the new IMAP account’s section in the sidebar.

If you have gigabytes of email to resync to IMAP, it can take a long time, even with a fast connection, because IMAP servers aren’t particularly efficient. This might be a good overnight operation after you get it started and make sure it’s copying as expected. Double-check your storage limits on the server, too, so you don’t exceed the maximum space, which can interrupt an upload.

For further reading

Joe Kissell’s Take Control of Apple Mail explains setting up accounts across Mac, iPhone, and iPad, as well as plugins, automation, and solving common problems.

He’s also got a new title out, Take Control of MailMaven, which explains the ins and outs of migrating and using a sophisticated, newly released email app.

[Got a question for the column? You can email glenn@sixcolors.com or use /glenn in our subscriber-only Discord community.]

Technically, the type we all used was POP3, the third version. ↩

We also liked pushing bits uphill 10 miles through the snow to the data center. It was uphill in both directions. ↩

Is a desk organizer for paper even so far in the past as to mark me as Very Old? ↩

This workflow became even better when—at a point I don’t recall—client email apps could mark messages as read on the server without deleting them. You could then see which messages were unread when you retrieved them from another device. ↩

Mail can detect some mail server settings automatically just by providing your email address. If you have problems or want to set it up manually, go to your host’s Web site and consult their documentation. IMAP typically uses port 993 for secure SSL/TLS connections. ↩