Possible server resource usage problems when using IMAP

When checking your e-mail account via an IMAP client, you might notice that things seem to hang from time to time. Sometimes 100% CPU usage or high memory usage could occur on your local computer, while it syncs mail from the server, leading to delays and possible freezing because of the intensive activity.

You might have also received a notice from our system administration department, that they've noticed elevated levels of usage on the server side coming from your IMAP activity.

When you check your e-mail on the server, you can think of this the same as having a post office box at your local post office. However unlike your traditional mail box, this post office box resides online so you can access it from anywhere.

 

How are you checking your email?

When checking e-mail, your e-mail client will present you with two methods or protocols for syncing mail from the server: POP3 or IMAP.

 

POP3 vs IMAP

 

With POP3 (Post Office Protocol) this would be the same as simply going into the post office, removing everything in your post office box and taking it home with you. You retain the physical copies of all of your mail that has been sent to you, and the post office (server) doesn't have to deal with them further.

With IMAP (Internet Mail Access Protocol) instead of simply taking everything out of your box and home with you every time. You instead grab a copy of each message, and the original stays in the post office box (server). This is convenient if you have multiple devices such as a desktop, laptop, smartphone, and tablet all trying to check mail from the same account.

 

When can using IMAP cause problems on the server?

Few messages = easy to sync

Lots of messages = difficult to sync

 

Inbox efficiency

Imagine for a moment going to your physical post office box to see if you had any new mail. It would be easy to see what mail is new, if you only had a handful there to choose from. However if you had a pile of over 2,000 pieces of mail sitting there, some old, and some new, it would be much more time consuming to figure out what is what and be on your way.

A similar scenario is encountered on the server when you're using IMAP. Each time your mail client checks for new messages on the server, it must first synchronize all of the messages headers of your entire Inbox folder. A message header contains some basic information about that message, so that you don't have to download the full message from the server until you actually click on that specific message in your mail client.

If you have only a few e-mails, the server can sync all message headers relatively quickly with minimal impact on the server's performance. However if you have thousands of e-mails in the Inbox, the server is going to have to do extra work just to let you know what messages are new.

 

Long term e-mail storage

 

What solutions are available?