eMail Synchronisation



What follows is what was presented at the June 2018 BMUG Members' Meeting about emails.

There is an explanation and then some extracts from a newspaper article that might be of interest.


'Protocols' is the name given by techies to the rules they agree to use to achieve a goal - eg to be able to share some data, or access something on a remote computer, etc. The two main protocols that have been used for email are POP and IMAP - POP3 is the current version of the 'Post Office Protocol' and IMAP stands for 'Internet Message Access Protocol'. Which of the two someone will want to use is, these days, mostly dependent on what the user wants to achieve. But, it should be noted, sometimes the user does not have a choice or does not know the difference.

To illustrate the difference, let's imagine a user has an email address This email address is being protected from spambots. You need JavaScript enabled to view it.. Remember that a user may have a number of email addresses and that each one will be provided by a service that handles email. The Gmail address is only one of our user's addresses - they also have This email address is being protected from spambots. You need JavaScript enabled to view it. and This email address is being protected from spambots. You need JavaScript enabled to view it., let's say.

Managing eMail

To access their mail, our user will need a 'mail handler' - some software (an app) that knows how to enable the user to work with their email. Most devices come with a built-in mail handler.

For simplicity, let's start with accessing Gmail on a Chrome Browser (or any other browser  such as Safari, Firefox, Internet Explorer, ...). If our user logs in to Gmail and works with their mail, they are, in fact, talking to a remote computer (via their browser) and telling that computer what to do with their mail. But most people don't want to work like this - they want their mail to be on their devices, available online or offline, and even to be synchronised across a few devices. This is where the difference comes in and what the systems do: they pretend things to the user so the user feels good and, behind the scene, they manage the problems (ie the software manages the problems).

If the user wants to be able to see the mail using different devices, there is an easy way to do this.

If the mail is actually left on the original computer of the service provider, then whatever device is used to look at it, the mail will look the same. That is, something managed on one device will automatically appear managed on all devices (that's what it should feel like). But in fact it will only be managed in one place - the service provider's compter and the user's software will be 'talking' to that computer and telling it what to do and then showing the result on the user's device. This is an IMAP service - the user has an app (software often called a mail handler) that talks to the mail system and everything actually happens on the service provider's computer.

BUT, as user, we often want to be offline etc - so our app has to know to get an up-to-date copy of the emails on to our computer (or phone or iPad) when it is online so that changes can be seen immediately. If something is added, it should show up whatever device is being used to look at the email and if something is deleted, it should not be seen anymore on any device. IMAP systems have clever extra tricks to make life feel better for the user - but at the core they depend on the emails being left on the service's server.

If the user wants to be in control of their emails, and to be able to work with them offline, they might choose to use the POP protocol. POP works by allowing the user's device to actually download the emails. That is, they are stored on the user's computer and taken off the service provider's system. The mail handler using the POP protocol will have the 'master copy' of the emails and when one is deleted from the user's computer, it is deleted. If it is composed on the user's computer, it can be sent using the same service as it was received from, or another, it doesn't matter. The POP user is not instructing the remote server to send a message but is making one itself and then sending it however it chooses.

BEWARE! these two scenarios are not quite accurate! Both IMAP and POP have evolved over time and they each do things that are more characteristic of the other, but of known popularity with users.

POP users can leave copies of their emails on the remote server and IMAP software often downloads emails in advance of their being requested just to make it easier for the user. But there is a trick in here - it is easy to leave so much on the server, either as a POP or as an IMAP user, that mailbox allowances are exceeded and the mail systems get cross!

When POP users download their emails, they download them to a single device and then they have the problem of synchronising them across all their devices. As this can be difficult, most users in this position choose to use IMAP systems. The default for many users, unknown to them but set by their mail handling software, is usually IMAP. Many people don't know about this, or worry about it, because their mail is 'safe with Gmail' or whoever!

But another problem for users is the archiving of emails. In what format is it best kept for the future? If the user wants to store emails for later reference, it's a good idea to extract them from whatever system and store them in mbox format. This is a simple format that can be used by most systems and so the emails will be available even when the technology changes. But importantly too, if the emails are stored in mbox format, they will be backed-up by Apple backup systems whereas otherwise when a Mac is backed up, the mail is not included.

Finally, if the user has more than one email address, and so needs to synchronise them, they can usually rely on their mail handling software to visit all the email servers and combine the emails, or they may choose to have their servers set up to send any in-coming mail (for whatever address) on to a particular server so all of it can be gathered from there (and stored there, if they use IMAP software).

The following is an edited version of an article published in the NY Times in 2017. See

 Managing Email on Multiple Devices

By J. D. Biersdorfer,

Q. How do I efficiently manage my email with three devices: computer, phone and tablet? Do I have to read, save, delete email three times, or can I easily sync them?

A. Most mail programs give you the choice of two ways to set up an account on a computer or mobile device — either with the IMAP (Internet Message Access Protocol) standard or POP (Post Office Protocol). If you want to keep your mailbox in sync across multiple devices, choose the IMAP method.

Compared with POP, IMAP is a newer technology for managing messages and handles checking the same mail account on multiple devices much more smoothly. With IMAP, even though you can see your mailbox in the mail program on your computer and devices, IMAP messages actually live on the mail server. When you read, delete or flag a message, you are performing that action on the mail server. The mail apps on your other devices see the change when you view the updated mailbox.

In contrast, most POP mail systems in their default settings download messages directly to the device that checks in at the time, and then deletes those messages from the mail server. When you check mail with your computer or other gadgets, those devices do not get the deleted messages, but they may download newer ones — which then get deleted from the server, making your mailboxes out of sync.

As a workaround, some mail providers allow you to keep messages on the server without deleting them automatically after they download, but then you have to repeatedly delete a message on each device. Additionally, the messages you send stay on the Sent mailbox of the computer or device that actually did the sending.

Most modern mail providers and programs support IMAP You can find instructions for setting up IMAP mail accounts for Google’s Gmail, Microsoft Outlook and Mozilla’s Thunderbird program on their sites. Apple’s iCloud mail does not support POP and uses IMAP by default.