Exchange ActiveSync (MobileSync) vs Good Old IMAP + SMTP

October 6th, 2014

Many years ago, it used to be that if you had a cell phone that had an email program included, you could configure using IMAP and SMTP to allow you to check email and send email…. just like how a desktop email program worked.

This is still the case, of course. However, as far back as 1996, Microsoft introduced the first version of “ActiveSync”, a protocol designed to allow mobile devices supporting it to synchronize email, calendars, tasks, and contacts with Microsoft’s Exchange server. ActiveSync has evolved over time, getting faster, offering support for use in every modern mobile device. While ActiveSync was designed to work with the Exchange server, these days it also works with other non-Exchange services that can talk the “ActiveSync language,” e.g. LuxSci through its Mobile Sync service.

In general, ActiveSync is much better than using IMAP and SMTP, though there are a few small corner cases where IMAP may be better for you. Below, we shall compare them from an end-user perspective … trying to shed some light on “which is better” from a practical point of view.

1. Device Setup


When setting up ActiveSync, you just need your username, password, and server name. After those are entered, you can select what you want to sync (e.g. email, calendars, tasks, contacts, notes).  Done.  Setup is quick and simple.


IMAP and SMTP have many more settings.  There are 1 or 2 server names with sometimes different usernames and passwords, depending on the provider.  There are various ports to choose from, options for secure or insecure connections, IMAP folder paths, different types of authentication methods, etc.  The options are rich and complex, and can lead to frustration unless the instructions you are using are tailored to your specific situation.

Winner: ActiveSync for simplicity.

2. Transport Security


These days, all ActiveSync connections are automatically and always performed over connections encrypted using SSL.  There is no choice and nothing to configure — its just secure (during data transport).


IMAP and SMTP can technically connect with or without SSL-style security.  It is up to your provider which security options are available to you and to provide you with instructions on how to set up your device appropriately.

If setup to use SSL and/or TLS, these connections have the same level of security as ActiveSync.

LuxSci, for example, enforces use of SSL and TLS on IMAP and SMTP by default, so you can’t set your device up “wrong” and end up with an insecure connection … this is not the case with all providers.

Winner: ActiveSync by a hair. While both provide the same level of security, ActiveSync makes it simpler to setup and thus it is more likely that you end up with a solid connection.

3. Checking Email

The email program interface looks the same when using ActiveSync or IMAP.  The difference is in how email can be checked and what email can be seen.


ActiveSync supports “Push” email.  When enabled, this allows your phone to be notified of and to download new email as soon as it arrives.  Push email is also very kind to the life of your device’s battery … meaning that you can get fast updates and have a long battery life too.  Push email is great.

If you don’t like Push email, you can still access email “on demand” or have your device check for new email “periodically,” just like with IMAP.

One downside of ActiveSync is that it may only show your recent email in each of your folders.  This can be a device limit and a server-side limit.  Some devices will show only email from the last week or month (this is sometimes configurable).  Sometimes it is a server-side limit.  E.g. LuxSci’s MobileSync will only synchronize the most recent 500 messages in a folder, for speed, efficiency, and mobile bandwidth reasons. If you really need ALL email, no matter how much that is, then IMAP is the way to go.


IMAP works great, but by default (e.g. on an iPhone), you can check for new email only “on demand” or have the phone ask the server for new messages up to once every 15 minutes.  E.g. there is no “Push” and the polling of the server is a larger battery drain than Push.

Some devices (e.g. Android, but not iPhone) do support something called “IMAP IDLE”.  This is a way for the device to hold open the IMAP connection and wait for the server to let them know about new email (and other changes to the folder).  From an end-user perspective, this is essentially the same as Push email; However IDLE does consume much more bandwidth and much more battery power than ActiveSync Push.

IMAP will check all messages in any folder that you look in.  This can be a distinct advantage over ActiveSync.

Winner: ActiveSync for Push email and battery friendliness.

4. Sending Email

The email program interface looks the same when using ActiveSync or SMTP to send email. The difference is in how email is actually routed.


With ActiveSync, outbound email messages are delivered to the server over the same secure ActiveSync connection being used to check email and synchronize calendars, etc.  This “just works”.


When using SMTP to send email from your App, a new connection is made to your provider’s SMTP server for outbound delivery of your message.  Due to the pervasiveness of SPAM, these outbound SMTP connections can often be blocked without notice by whatever ISP, cellular, or Wifi service you are currently connected through, resulting in errors and an inability to send your email.

To get around this issue, some email providers like LuxSci offer “alternate” ports to configure in your phone for sending email in a way that will be allowed.  LuxSci, for example, has lots of extra ports in addition to the standard one (port 25).  E.g. 80, 465, 587, and more.

However, even with the option to use alternate ports, SMTP is a recipe for aggravation.   You will likely set up your phone with one port that works and find that 3 months later it doesn’t (due to settings in your network that you have no control over) and you need to change ports.  Yes, you may be able to resolve the problem.  But it is still extra time and stress that no one needs.

Winner: ActiveSync for not needing to worry about ports.

5. Remote Wipe


ActiveSync allows you to “Remote Wipe” your phone.  E.g. if it is lost or stolen, you can issue a command from a user interface that will delete data off your phone if it is ever enabled again.  This is very good for your security and privacy.


There is no such functionality with IMAP and SMTP.

However, many mobile phones now have other free options for enabling Remote Wipe … so ActiveSync is not really needed.  For example: iPhone and Android.

Winner: ActiveSync, barely.

 6. Synchronizing Calendars, Contacts, Tasks, and Notes


ActiveSync allows you to synchronize your calendars, contacts, tasks, and notes with your provider’s server.  These can and often are different from your personal calendars, contacts, tasks, and notes.

E.g. I have my personal calendar synchronized through iCloud but my work calendar and contacts synchronized through ActiveSync with our office accounts which are then also synchronized with my co-workers phones.  I could not do that with iCloud unless everyone used the same Apple Id… which might be fine for a home environment, but is a no-go in a work environment.

This synchronization service “just works” and includes “Push” updates … so changes appear on your phone in real time without significant battery drain.  It doesn’t get much better than that.


There is no such functionality with IMAP and SMTP.

Winner: ActiveSync. This is the most significant reason of all to use ActiveSync.

 The Winner?

The clear winner is ActiveSync. Given the choice, the only significant reason that you might consider IMAP is if you have very large folders and need to access all email in these folders from your mobile device — not just the recent ones.